The overriding purpose of any forensic investigation is to apply the scientific method to the investigation of a crime, and in the process collect the facts, results, and proof to serve as evidence that can be presented in a court of law. One of the most important and influential types of evidence that can be presented in court is photographic evidence and other types of visual forensic documentation. Anybody, whether or not they are a forensic scientist, can verbally describe a scene or the conditions of a crime, but showing a photograph or a video of that scene to the court is far more valuable, because, as the saying goes, “a picture is worth a thousand words.” By using correct forensic documentation at a crime scene or in a laboratory, the forensic scientist is also able to remove any inherent bias (either intentional or unintentional) in their presentation to the court. The proper use of a photograph should go hand in hand with the forensic case notes, crime scene sketches, and other written forms of documentation in the case, and all of the documentation should serve to highlight, explain, and clarify all of the evidence in the case. In a courtroom setting, though, the photograph, video, or other graphic documentation provides that necessary visual aid, and brings the court into that critical moment in time that was captured and preserved in the proper forensic manner.
So what differentiates normal photography from forensic photography? Well, to begin with, the basics are all the same. A camera is used to collect and focus light onto a film surface, which, depending on the settings of the camera and the type of film used, captures some aspect or detail of what is being photographed. In forensic photography, though, the goal of each photograph is to reveal, highlight, and document the evidence for the case in as much detail as is necessary. Because no two crimes or crime scenes are ever the same, there is also no single manner or way in which photography “must” be used at such scenes. A forensic photographer must be ready to document several different aspects of a crime in many different ways. Also, depending on the size of the forensic crime scene unit or forensic lab, there might be a single person or a team of people dedicated to photography, but all good forensic scientists should know the basics of forensic photography and be able to apply that knowledge in all types of circumstances and locations.
One location that forensic photography is useful is a hospital or autopsy room, where documentation of wounds, bite marks, lacerations, and abrasions must be freshly documented before they are treated (on a living victim) or dissected further (as is done in an autopsy). Because these photographs are used to document pattern injuries, a high-quality camera should be used so that fine detail of the wounds is not missed.
Unfortunately, many emergency rooms do not have the time or budget to retain a full-time forensic photographer or train nurses and doctors in the proper aspects of photography. Even worse, such emergency rooms routinely use Polaroid instant cameras because of the ease of use and rapid development of the photograph. These cameras usually have poor film quality for capturing high-detail photographs, and they are also incapable of close-up photography that is necessary when dealing with bite marks, which are commonly encountered as evidence in crimes.
In the past, forensic documentation of bitemark evidence was troublesome, not because the photos were of poor quality, but rather because teeth, three-dimensional objects, were being compared with two-dimensional photos. If the photos were not taken at directly 90 degrees to the bitemark evidence, there would be a shift in the measurement of the bitemark in one direction, and without a reference in the photo to measure this shift, a comparison of the bitemark to a suspect’s teeth could not be made. This changed with the creation of the American Board of Forensic Odontology (ABFO) No. 2 scale. The ABFO No. 2 scale is an L-shaped ruler with crosshair circles at the ends of the “L” and in the corner, as well as a full standard and metric ruler (see Figure 4-1).
Figure 4-1 The ABFO No. 2 scale
When placed next to a bitemark and photographed, the scale not only provides the necessary measurements in both directions, but the crosshair figures can be measured in the resulting photograph and the angle at which the photograph was taken can be determined. If, for example, the photograph was taken at an exact 90-degree angle, the crosshair circles will be perfect circles in the photograph. As the camera is tilted, perhaps to a 45-degree angle, the crosshairs in the photo will be distorted, appearing as ovals. The geometric change in the circle directly corresponds to the angle of the camera, and the bitemark evidence can therefore be calculated at its true measurements and compared against the suspect’s teeth in the case.
A second common location for using forensic photography is the forensic lab. As evidence is opened and examined in the lab, it is necessary to document the state and condition of the evidence, as well as the packaging that it arrived in. As the evidence is examined, close-up photographs may be necessary to further document minute details of the evidence or highlight areas that are selected for testing. Also, as testing proceeds and swabs, cuttings, and scrapings are taken from the evidence, it will be necessary to document the physical cuts, scrapes, and areas on the evidence that were tested or altered during the examination. These photographs will then be incorporated into the lab notes for the evidence, and might even be labeled by the casework analyst, perhaps to point out particular stains, marks, indentations, or minutiae that identify and individualize that evidence. Forensic photography is of particularly unique importance in a fingerprint analysis lab, where the photograph of the fingerprint itself will be scanned into a computer for comparison to the AFIS national fingerprint database.
While there are other locations apart from hospitals, autopsy rooms, and labs that require the use of a forensic photographer, the most prominent location for forensic photography is the crime scene. Because time is always a factor at a crime scene, it is important for the scene to be photographed in its entirety early on and then sequentially as the scene is processed over time. That way, there will be a standing record of the progress of the work that was done at the scene as well as photographic documentation of the changes affected on the scene by the presence of the crime scene personnel.
Photography at the crime scene is also necessary for the documentation of the evidence in its original state before it is collected and removed from the scene. Even though the evidence will be further documented later on, the relationship of that piece of evidence must be established at the scene with a series of photographs. Those photographs are known as establishing photographs, and serve to cover the scene from a wide angle or distance and place the scene in relationship to a landmark, address, or some other general location. For example, for a crime scene at a house, a series of establishing shots would be taken of the outside of the house and would include the house address, the street signs and addresses, as well as the conditions of the exterior of the house, the street, the lawn, and so forth. Moving inside the house, more establishing shots can be taken of entire rooms or floors of the house to capture as much of the scene as possible in one overall photograph. Although lighting, the use of flashes, and the basics of photography are necessary for these photos, no scales or references are needed in these establishing shots. Additionally, there should be a brief written description of what is being photographed for each photo recorded in a photo log.
The second type of forensic photographs taken at a scene are midrange shots, which in effect “close in” on the actual details of the scene without losing the ability to place the evidence in relationship to the location. For example, if the establishing shot of a room was taken from a corner, the midrange shot might be taken closer to the spot in the room where the evidence is located. Midrange shots are useful for documenting the overall condition and location of evidence at a crime scene, and measurement scales should be used to begin to serve as a reference of size and distance in the photos. When using measurement scales in forensic photography, there should always be at least two scales in each photo, with one scale laying perpendicular to the other. This is necessary to allow the length and width of the evidence to be accounted for in each photograph, as well as to serve as a reference for the angle at which the photo was taken (for more on this, see the “American Board of Forensic Odontology Bite-mark Scale” section above). It is important to note here that midrange shots can be taken at any angle necessary to properly document all aspects of the evidence and conditions at the crime scene. Also, at this point, a forensic photographer should be working side by side with a crime scene investigator in a thorough search and analysis of the scene, documenting any and all evidence that the crime scene search reveals. When necessary, close-ups, or detail photographs, should be taken.
Detail photographs at a crime scene are taken to document the fine details of the smaller aspects of the evidence at the crime scene, and to capture these details in a specific way. For detail photography, it is again necessary to utilize the two-dimensional scale approach, but at this point detailed photographs should be taken at a 90-degree angle to the evidence. Also, since these photos should be capturing the fine detail of the evidence, proper lighting is critically important. Depending on the circumstances, it might also be important to photograph the evidence in a 1-to-1 ratio. When taking a 1-to-1 photograph, the focus of the lens is locked so that the image size on the film will be exactly the same size as it is in real life. 1-to-1 photography is commonly used when photographing fingerprints at a crime scene before they are dusted, and again after they are dusted but before they are lifted. The resulting photograph slides can then be directly scanned into the AFIS fingerprint database and their size will be exactly the same size as they occurred in real life.
To ensure that evidence is documented correctly, a forensic photographer needs the proper equipment. However, the best cameras, film, filter, flashes, and lenses are useless unless the photographer knows how to properly utilize these components to their full advantage. This combination of knowledge and specialization are critical so that the forensic photographer can capture for perpetuity all the necessary details about the crime scene and/or the evidence.
The basic photographic equipment setup for any good forensic documentation consists of a basic medium-to-large format camera with a variety of lenses, a good flash, backup batteries, a variety of filters, and of course film. The typical film that is used for forensic purposes is standard 35mm film. 35mm film is measured across the width of the entire negative film, so that a basic negative image has a typical 2:3 width-to-length ratio. Film can also be black-and-white or color, and one type of film may be preferred over another sometimes when photographing certain aspects of a scene. There is even a special type of film that is only sensitive to infrared heat, and is used in special circumstances.
Black-and-white film, which is also referred to as monochrome film, is very good at documenting contrast differences. Contrast can be thought of as the varying degrees of lightness and darkness of an object, surface, or a light source. Contrast photography, in forensic terms, is therefore used to highlight the differences of one substance on another in terms of evidence, such as a dusty footprint on a dark floor, or a greasy fingerprint on a television screen. Filters can also be used to help enhance the differences in contrast, and as a result can have an additive or subtractive effect on the resulting photograph. For example, if a blue filter is placed over a lens and a photograph is taken of a bloody handprint on a blue wall, in the resulting photograph, the wall will be much lighter and the red handprint will be much darker. This is because color filters lighten up their same colors while darkening their complementary colors in contrast photography. A complementary color can be thought of as the subtractive color to any other color; when the two are mixed, the result is a darker color that “cancels” out both of the original colors. For example, green and magenta are subtractive colors, as are blue and yellow, and red and cyan. Using this principal in black-and-white contrast photography can help highlight images on the resulting photos by using color filters. Color photography, on the other hand, is used extensively to document the basics and overviews of a scene, but can also be used to show the differences in the contrast of colors of evidence at a scene or in the lab. For example, a high-quality color film with a large degree of contrast helps to show dark-red bloodstains on a black or dark-red background, whereas they would not be clearly seen with the naked eye.
Another important aspect of film is the speed of the film, which is commonly known as the ISO of the film. ISO is a short term for the International Organization for Standardization. ISO is not an acronym, but a modification of the Greek word isos, which means “equal.” The ISO of film is an international standard that measures the sensitivity at which the film surface collects light. To understand this, it is important first to understand what film is and how film is produced.
Film itself is made up of several components, the main being the actual thin plastic backing that supports the negative. The second component of the film is a gelatin layer, which is adhered to the plastic and holds the final layer in place. The final layer is an emulsion of silver halide salts. The silver halide is light sensitive, and is white until it reacts with photons to turn black. The size of these silver halide salts change from one type of ISO film to another, such that a “slow” film uses smaller grains of salt that require more light and a longer exposure time, and a “fast” film uses larger grains of salt that quickly collect light and require a shorter exposure time. Therefore, the ISO of the film is actually a measure of not only the “speed” of the film but the grain size of the film as well. For this reason, “fast” films tend to have more “grainy” photos, as the result of the large grains of silver halide, whereas slower films tend to display higher levels of detail, clarity, and sharpness (assuming the photo was taken correctly) due to the smaller grain size. This ISO measurement applies equally to both monochrome and color film, and therefore it is important to have an assortment of different types of ISO films on hand when taking forensic photographs.
While the speed of the film is important to keep in mind, the amount of available light and the speed of the shutter on the camera are also key elements in capturing a quality photo. While there is a large variety of camera models, styles, and types commercially available, the standard camera that is used in forensic photography is an SLR, or single-lens reflex, camera. Figure 4-2 depicts the standard features of an SLR camera.
Figure 4-2 The typical features of an SLR style camera
This type of camera directs the image that is seen through the lens to the viewing eyepiece on the top of the camera using a 45-degree mirror that is positioned in front of the camera shutter. This is known as “through-the-lens” (TTL) focusing, because what the photographer sees in the eyepiece is exactly the same image that will be captured on the film. In other types of 35mm cameras, such as the common point-and-shoot varieties, the viewfinder lens is separate from the actual lens of the system. The image that the photographer sees through the eyepiece of these point-and-shoot cameras is not the same image that will be captured on the film, due to the offset of the film lens and the viewfinder lens. Therefore, this style of point-and-shoot camera is not desirable for forensic purposes.
In an SLR camera, as a photograph is taken, the 45-degree mirror is pulled or pushed up and out of the way of the light path so that the entire image is captured on the film when the shutter opens. The speed at which the shutter operates is known as the shutter speed and is measured in fractions of a second. The faster the shutter opens and closes, the less light that is transmitted to the film’s surface; the slower the shutter operates, the more light that is transmitted. Interestingly, as shutter speed is increased from one setting to the next, the amount of light allowed to pass is exactly halved. But, as the shutter speed is decreased from one setting to the next, twice as much light is allowed. Therefore, it is useful to coordinate the shutter speed with the ISO of the film that is being used to achieve the optimum exposure of the image on the film.
Another nice feature about SLR cameras is that most models allow for the quick interchange of different styles and types of lenses. This enables a photographer to use one camera body and interchange several different lenses depending on the necessary shot. Therefore, in forensics, the initial establishing shots can be done with a wide-angle lens, the midrange shots can be done with a medium-format lens, and the detail shots can be done with a close-up, or macro, lens. The major difference in these lenses is the focal length of the lenses, which is the distance from the lens to a point where parallel light is brought into focus.
The aperture, or the opening of the lens, is another key element that can affect the development of photographs. The aperture is actually a circular ring that can be opened or closed to allow more or less light through the lens, similar to the iris of your eye. When the aperture size is correlated against the focal length of the lens, this is known as the f-stop. The f-stop on most SLR lenses is expressed as a number, typically as f/#, where f/# is equal to the aperture divided by the focal length. When f/# is small, the aperture is wide and more light is allowed though the lens. When f/# is larger, the aperture is small and less light is allowed through the lens. This affects not only the exposure and development of the image on the film, but also the depth of field of the photograph. The depth of field is a measure of what is in focus surrounding the subject being photographed. The larger the depth of field, the more in focus the surrounding objects in the foreground and background will be in a photograph. The smaller the depth of field, the less in focus the surrounding objects will be. This is directly correlated with the aperture of the lens, such that the smallest aperture (and therefore largest f/#) produces the largest depth of field, and the largest aperture (and therefore smallest f/#) produces the smallest depth of field. Aperture is also based on a logarithmic scale, not a linear scale. Therefore, when you move from the smallest f-stop to the next one up, you halve the amount of light that is allowed to pass through the lens. Conversely, if you start at the largest f-stop and move down, you double the amount of light passing through the lens (see Figure 4-3).
Figure 4-3 Shutter speed vs. aperture scale
In the end, the aperture and the shutter speed have the most critical roles in capturing a quality photograph. Because the change in either direction of either the aperture or the shutter speed can halve or double the amount of light, it is sometimes not clear which setting will be best, and a photographer might choose to bracket exposures of one set of shots. Bracketing is a process in which a successive series of photographs is taken but each photo has one change in either the shutter speed or the aperture, but not both. The reason for not changing both is that if the aperture of the lens is moved up one f-stop (to let through one-half of the light) and the shutter speed is decreased (to let twice as much light through as before), the photo would be the same as the previous photo, because the same amount of light overall is still hitting the film. Bracketing only one of the settings enables a photographer to capture the correct photograph in a group of shots.
Another critical aspect of photography is the proper use of lighting and flashes. Because photography is nothing more than using light to create images on film, it is absolutely necessary for the proper lighting to be available when shooting a photograph. Sometimes, this is achieved by using sunlight and either direct or indirect shading to provide the correct levels of light for the photos. However, for crime scenes that are indoors or photographed at night, a forensic photographer must rely on other light sources, such as lamps, strobes, and flashes, to properly illuminate the evidence that is being photographed. The use of flashes is very common in all types of photography, but in forensics, it is important to keep the flash from interfering with the outcome of the final photograph. Flashes can interfere by either under- or overexposing a photograph if used incorrectly, or can create glare on a surface, which can mask the actual evidence in a photograph. These common lighting problems can be easily avoided with the use of ring flashes and oblique lighting when photographing evidence.
A ring flash is a type of flash that attaches to the end of the lens and surrounds the lens. This is useful in midrange and detailed forensic photography, because it limits the distance of the flash to the object being photographed and can cut down on the amount of glare and bounce that is created by normal flashes. Also, if the object that is being photographed is close to the lens, a normal flash might not illuminate the object due to the angle of the normal flash to the object. Using a ring flash therefore creates a more even and flat flash effect, and in effect can produce shadowless figures. This means, from a forensic standpoint, that the image captured on film will be as realistic as possible and not look like an object photographed with a normal flash.
Oblique illumination is not a type of flash, but rather is a special technique that can be used with a standard flash on an SLR camera. Oblique illumination requires that the flash be connected to the camera by a cord or flash trigger so that the flash can be held off to the side of the object being photographed. When the photo is taken, the flash off to the side sends oblique light across the surface of the object rather than directly at it. The benefit of this technique is that the surface of the object “bounces” random photons of the oblique light back toward the lens, allowing the photo to show the contours and details of the object’s surface that otherwise would not have been visible. A good example of this can be done by planting a fingerprint on a clear, flat surface, like a CD jewel case or the lens of a pair of glasses. If you then take a flashlight and point it straight at the print, you might have trouble making out the fine details of the ridge patterns. However, if you hold the flashlight at an oblique angle to the printed surface, the light acts as an oblique illuminator and you can see the fingerprint much easier (see Figure 4-4).
Figure 4-4 Oblique light vs. scattered and reflected light
One final aspect of flashes and illumination to discuss is a handy technique known as “painting with light.” This requires at least two people and a very steady camera tripod. Consider a dark night scene or pitch-black indoor scene that requires establishing shots but has no major light sources, lamps, or strobes available. If a single flash is available, then there is no problem. Simply mount the camera on the tripod and set the shutter to remain open until the trigger is pressed a second time, or have the second person hold the shutter open manually. By holding the shutter open indefinitely, the film is exposed to any and all light at the scene, so the lens might need to be temporarily covered with a black card by the second person as well. As the first person mans the camera, another person simply walks around the perimeter of the scene, firing the flash every few feet. As the flash is fired, the lens is uncovered and the flash burst “paints” the scene on the film. As the general area of interest is painted with light, the final image will show what appears to be the scene fully illuminated, with bright flashes in the background where the person working the flash was standing!
On a final note, all photography, forensic included, relies on the proper white balance and color temperature in all of the photographs for accurate and realistic reproduction of true-to-life images. Color temperature of light is based on a “theoretical black-box radiator” that gives off a certain color based on the amount of energy, in Kelvin, that is supplied to the box. As an approximation, natural sunlight is around 5500 Kelvin, and most flashes, lights, and other photographic illuminators strive to achieve this same color temperature with their lights. White balance in photography is therefore a measure of the color temperature and how it affects the “color” of white. At 5500 Kelvin, white is absolute white, but as the color temperature drops, white can become yellowish-red, and as it increases, white can become blue. Finding this balance and correcting for it can be achieved by photographing an 18 percent grayscale card to calibrate the internal light meter of the camera or an external light meter, if necessary.
The recent advancements of digital cameras, along with their decreased cost, have made many people take notice of the advantages of digital imaging over that of traditional film. In the forensics field, however, there are issues with using digital photography that have both positive and negative effects on the documentation of evidence and crime scenes.
To fully understand the reasons for and against digital photography in forensics, it is important to understand what the differences are between digital and film cameras. In a majority of the digital cameras on the market today, a charge-coupled device (CCD) chip has replaced the film, and images are stored on media cards or in the memory of the camera itself. The CCD chip is a photosensitive device that captures and records the image that is focused onto the surface of the chip. The CCD chip is not one device, but instead a series of millions of photosensitive receptors. The overall image quality of a digital photograph is determined by the size and number of receptors on the CCD surface. Because each receptor accounts for a single pixel, or dot, of the digital image, the quality of a digital camera is measured in megapixels (1 million pixels). Therefore, the higher the quality of the digital camera, the more megapixels that are available on the CCD. Since there are limitations to the total size of the CCD chip, as the number of megapixels goes up, the relative size of each of the photosensitive cells on the chip gets smaller. To compare this to film, the megapixel count is much like the ISO of the film. The average ISO 1000 film image is therefore around 7–8 megapixels, and most inexpensive digital cameras are still in the 6–7 megapixel range today, while the higher-quality digital cameras are around 8–9 megapixels.
The images that are processed and stored in a digital camera are usually in some common graphics format, such as .jpeg, .tiff, or .bmp, depending on the settings and the quality of the camera. Because the images are stored in memory after they are captured, many digital cameras have a small LCD screen on the rear of the camera that allows the user to view the image after it is taken. This is extremely helpful when trying to capture a difficult image, and the instantaneous feedback can be used to adjust the camera settings and reshoot the image if it is not successful. Also, some of the point-and-shoot digital camera models use the LCD screen as a view-finder, eliminating the need for the offset viewfinder and allowing the user to “see” through the lens as if the camera were an SLR-style camera. Since the images can be immediately reviewed, the use of digital cameras has all but eliminated the need for bracketing a series of photographs.
The photographs themselves also not only contain the images that were captured by the camera, but most digital cameras also automatically include a data file with each photo. This data might include a time-and-date stamp and readout of the settings that were used on the camera to shoot the image. Some cameras even have indicators of the levels of white balance and contrast as part of the information of the image. Since these images are in a purely digital form, they can be uploaded or downloaded to a computer for viewing, printing, or editing. They can also easily be deleted from the camera, memory card, or computer hard drive.
While all of these issues seem to be benefits that support the use of digital photography in forensic science, several of them are subtle problems that can have massive implications in the proper documentation of evidence. First and foremost, there is a major problem when attempting 1-to-1 photography with a digital camera. A majority of digital SLR cameras use a CCD chip that is smaller than typical 35mm film, and therefore the image after processing is also smaller than the original image when shot at 1-to-1 with a locked lens (see Figure 4-5). For this reason, most cameras have a correction factor that is published in the manual, and this factor needs to be multiplied by the lens lengths to establish what the true 1-to-1 should be. For example, if the correction factor for a CCD is 1.5, a 24mm lens will actually act more like a 36mm lens (24mm × 1.5 = 36mm), and this adjustment needs to be considered when shooting all types of digital photographs. Recently, however, a few high-end, professional SLR digital cameras have come out that have a true 35mm-size CCD that is capable of true 1-to-1 photography, but these are expensive.
Figure 4-5 1:1 photography on film compared to digital
The cost of digital photography also needs to be considered when addressing the needs of a forensic department. While the use of digital cameras eliminates the expenses of film and film processing, digital cameras tend to be more expensive than regular film cameras, and this is especially true with the digital SLR models that are on the market. Also, unlike film cameras, digital technology is constantly getting better and better, such that if a forensic lab were to invest in a digital camera system, it would be obsolete in a very short period of time. Therefore, the cost of keeping up to date with the current technology may be prohibitive to many forensic laboratories.
There are also limitations to digital photography that cannot be overcome with technology. Currently, there are very few digital cameras that capture true monochrome (black and white) images. Most digital cameras simply “turn off” the color sensors on the CCD chip, capturing only the contrast differences of an image, but as a result the sensors that are turned off reduce the overall image quality by half or better. Also, there is no digital CCD chip in any current digital camera that captures infrared images, and this is occasionally a useful tool in forensic photography.
Another factor to consider with digital photography is that the images need to be archived and backed up on a computer system. Because digital photo files can be very large (several megabytes), a modern computer system or network with adequate storage capacity is necessary to maintain the proper archiving and storage requirements. This same issue also applies to film photography, but 35mm slides are easily stored in a variety of ways, from books to carousels to canisters, and since processed film is stable when stored under proper conditions, there is no need for redundant backups.
Finally, and perhaps the most controversial issue surrounding digital forensic photography, is the fact that digital images can be easily manipulated. Using readily available programs like Photoshop or other image-editing software, a person can do anything from remove red-eye to add false elements to a digital photo. Likewise, there are specific enhancements that can be done to a digital image to highlight, clarify, or magnify key elements in a photo. Both of these actions have benefits as well as disadvantages in forensics. Obviously, if the use of a software program can help enhance a bloodstain on a dark background, this is helpful. At the same time, the falsification of evidence in a photograph is a major problem.
While there are ways of detecting such manipulations in digital images, the recent advancements in digital editing software can make such changes imperceptible to the untrained eye. As a result, there is a growing concern that an unethical forensic scientist could “digitally” plant a fingerprint or bloodstain in a crime scene photo to bolster the evidence in a case. While there would be dire consequences for any forensic scientist caught doing such an outlandishly unethical act, it does not mean that the concern is unfounded. Currently, the FBI and the American Academy of Forensic Sciences have both established guidelines based on the Scientific Working Group on Imaging Technology’s (SWGIT) recommendations for the preservation and documentation of digital evidence. These guidelines form a basic plan that enforces a protocol for digital image authentication, management, and security. In general, the guidelines propose that the original image be preserved, and any manipulation or enhancement that is performed on the image be logged and documented in a forensic manner. In the end, any image that is presented should be annotated as an “enhanced” or “modified” image, and should be shown alongside the original, unaltered image. As digital photography becomes more advanced and the issues surrounding the use of digital cameras are resolved, these guidelines will need to be modified and solidified to ensure that unscrupulous actions are not taken with the images, and that the use of digital photography can be a reliable and valid form of forensic documentation.
While photography is the most common form of visual documentation used in forensics, other forms are commonly used as well, and in the end they also serve as a visual medium for collecting and preserving the conditions of the crime scene and the integrity of the evidence. One such form is forensic videography, or the use of a video camera to capture moving images over a period of time. While it may seem out of place to consider the use of a video camera or camcorder at a crime scene, it is important to realize that video cameras are commonly used in police cruisers. These cameras not only record the activities of a police officer to ensure that proper procedures are followed, but also record the license plates and vehicle makes and models of the cars that are pulled over. Although this video might not follow the “rules” of proper forensic documentation, it is nonetheless admissible in court and can serve as evidence in an investigation. In the same way, a video camera at a crime scene can be used to document the scene over time as well. The use of a video camera at a crime scene can help in recording the spatial relationships of different areas of the scene, by “walking” the camera through the entire scene. As this is done, the video can provide another overview of the crime scene and begin to highlight key areas of the scene that might be critical to the investigation. Also, just like overview photography, the video can show the changes and interactions at the scene and serve to record the actions of the forensic investigators. It is very important to note that videography should never replace the use of photography at a crime scene; a video camera is simply another tool for general documentation. Videos tend to be grainy and noisy, so it is important that overview, midrange, and detail photography still be done for proper forensic documentation.
Another form of visual documentation can be done with surveying equipment, especially the use of computerized line machines and GPS-linked surveying optics that can map a crime scene. One such machine is designed to capture a 360-degree view of a crime scene, and by plotting key locations, such as building walls, fences, and trees, it can create a three-dimensional computer model of the crime scene. This can be extremely useful when dealing with outdoor crime scenes that cover large areas, and where wide-angle photography alone will not properly account for the establishing shots. Other types of surveying equipment use lasers and distance-determining calculations to form 3-D models of locations or objects at a scene. For example, stairwells, which can be difficult to properly document in photographs, can be mapped in 3-D using the laser rangefinder machine, and a computerized model of the stairwell can be used to map the major locations of the evidence in the case and supplement all the photos of the stairwell as well. As always, as was the case in videography, these surveying tools should never be used in place of photography, but should help by bringing together a crime scene and establish more of an overview than a 2-D photograph can provide.
Another important aspect of forensic photography is the analysis of forensic images. There are times that the crime scene or evidence is no longer available to the analyst, and all that is left are the photographs, videotape, notes, and other documentation from the crime scene. If all of the documentation was done correctly, and adheres to the proper forensic protocols, there is no reason that the photos and other items cannot be used to analyze and completely re-create the original crime scene. One of the most common practices in forensic crime scene analysis is the reconstruction of the events of the scene by using blood-spatter or ballistic-tracing analysis. If the original photographs were taken properly, the reconstruction of the trajectory of the blood or bullets can be done to find the origin of the spatter or gunshot. The reconstruction can be accomplished by scanning the original photograph into a computer, or the trajectory lines can be directly traced on a copy of the original photograph. Likewise, the photographs themselves can help an investigator who was not at the actual scene get a first-hand look at the original state of the evidence before it was collected, packaged, and shipped to the laboratory.
A second type of forensic image analysis is an in-depth analysis of the image itself. By using high-resolution scanning and close-up photography on suspected forged or hoaxed images, the modified and edited regions can stand out in a photograph and prove to a trained image examiner that there was some type of manipulation of the original image. Other times, it might be necessary to enhance faded images or re-create missing areas of photographs as well, and there are a variety of software programs that allow for the forensic reconstruction of these images. Because this is considered manipulation and enhancement of digital evidence, the guidelines concerning the proper forensic documentation, preservation, and annotation of the images must be followed.
Forensic image analysis can also be applied to video and other types of motion-picture film. It is a routine practice for automotive safety engineers to use highspeed video to capture the results of crash-test experiments. The results of these videos upon playback allow the engineers to perform a slow-motion or even frame-by-frame analysis of the damage sustained to both the vehicle and the crash-test dummies inside the car.
Sometimes, the videos or films of events that are intended to be nothing more than basic documentation are used later on for forensic purposes. This was readily the case during the investigation in 2003 into the loss of the space shuttle Columbia. Cameras on the ground recorded footage of a piece of foam insulation breaking free and impacting the left wing of the shuttle. This impact caused a breach in the heat shield of the orbiter, and as a result, during re-entry into Earth’s atmosphere, superheated air seeped into the body of the shuttle, melting the aluminum frame and destroying the shuttle, killing everybody on board. Following this disaster, an extensive review of the camera footage identified not only the exact location from which the insulation broke free, but also the exact location where it struck the body of the shuttle and exactly what heat-protection tile was damaged that led to the fatal final re-entry of the space shuttle.
The same type of image analysis most famously has been applied to the images of the assassination of President John F. Kennedy. The Zapruder film, named after the man who shot the film, Abraham Zapruder, records the final moments in the life of President Kennedy on November 22, 1963. The Zapruder film contains only 27 seconds of 8mm film, but has become one of the most widely analyzed pieces of footage in the world. Despite the grainy nature of the film and the rudimentary style of camera it was shot with, there are very clear moments in the film that show the fatal shots hitting President Kennedy as he rode in his car through Dealey Plaza in Dallas on that day. These individual scenes were scrutinized not only by the experts on the Warren Commission (the unofficial name given to the President’s Commission on the Assassination of President Kennedy, based on the name of its chairman, U.S. Chief Justice Earl Warren) in the 1960s, but also by several other analysts over the years that have contributed to the debate over the events and circumstances surrounding the assassination. While the Warren Commission has used the Zapruder footage to bolster the idea that Lee Harvey Oswald acted alone and fired two fatal shots, other experts have used the same footage to show the impossibility of a “single bullet theory” and point out inconsistencies in the actual footage as well. Despite the forensic applications and increases in technology, the analysis is limited by the length and quality of the original footage. As a result, the controversy surrounding the Kennedy assassination and the Zapruder footage will likely continue well into the future.
Refer to the text in this chapter if necessary. Answers are located in the back of the book.
1. A wide-angle lens has:
(a) A narrower angle of view than a telephoto lens
(b) A longer focal length than a normal lens
(c) A wider angle of view than a normal lens
(d) A longer focal length than a telephoto lens
2. Focal length is defined as:
(a) The equidistant point of focus between the lens and image
(b) The distance from the lens at a point where parallel light is brought into focus
(c) The distance from the lens at a point where oblique light is brought into focus
(d) The distance from the lens to the plane where the object is brought into focus
3. In film photography, the silver halide salts turn black by which method?
(a) Exposure of the sliver emulsion to photons of light
(b) Processing the film in developer
(c) Fixing the latent image in fixer
(d) Washing the film in acetic acid
4. A telephoto lens has:
(a) A longer focal length than a normal lens
(b) A shorter focal length than a wide-angle lens
(c) A shorter focal length than a normal lens
(d) A wider angle of view than a normal lens
5. In establishing photographs of a crime scene, what is required to be in the photograph?
(a) The area of interest around the crime scene
(b) The areas where detailed photos will be taken later on
(c) A landmark
(d) All of the above
6. What color of color contrast filter would be used to enhance a bloody handprint on a blue wall?
(a) Red
(b) Blue
(c) Green
(d) Orange
7. In digital cameras, the acronym in “CCD chip” stands for:
(a) Closed-circuit diode
(b) Camera-card device
(c) Charge-coupled device
(d) Current-carrying digit
8. To cut down on the amount of glare and bounce from a normal flash, one could use:
(a) An oblique flash
(b) A ring flash
(c) Natural sunlight
(d) All of the above
9. SLR stands for:
(a) Single-lens reflex
(b) Standard-lens recoil
(c) Single-laser reflection
(d) Side lacking ridges
10. Most digital cameras can mimic every aspect of film photography except:
(a) Zoom photography
(b) Wide-angle photography
(c) Flash photography
(d) Infrared photography
