Lt. James O. Pex
Oregon State Police
Coos Bay Forensic Laboratory
Documentation by photography is an important and powerful tool in the investigation of domestic violence crimes. When injuries resulting from domestic violence are promptly and adequately documented, it is possible for prosecution to occur without the victim’s testimony.
Often, victims of domestic violence are dependent upon the abuser for food and shelter. If the abuser is only jailed temporarily after the initial arrest, it is possible for an abuser to coerce the victim into not testifying. Therefore, the importance of documentation becomes relevant in preventing the recurring abuse of victims. The pictures can be used in the event that the victim later becomes unwilling to testify.
The objective this article is to provide some basic knowledge of photography and illustrate four photographic techniques that have proven to be successful in domestic violence cases: color photography, alternative light source (narrow band light source) photography, reflective ultraviolet (UV) photography, and infrared (IR) photography. In addition, affordability of the necessary equipment is a concern, and the illustrated techniques were developed with this in mind.
The Light Spectrum
The colors that are visible to the eye represent only a small portion of the light spectrum, also known as the electromagnetic spectrum. Visible light, or white light, is a combination of all the visible colors. A beam of white light can be separated into the visible spectrum using a prism. The band of colors range from violet to blue, blue-green, green, yellow, orange, red and deep red. Each color represents a different wavelength of light. These wavelengths increase in the direction from blue to red along the length of the spectrum. The visible region of the light spectrum ranges form 400 to 700 nanometers (nm) in wavelength.
The areas extending in either direction beyond the visible spectrum are the invisible regions of light. Below violet from 200 to 400 nm is the ultraviolet region. Although we cannot see this light, it is reactive with photographic materials. Therefore, it is possible to produce images that may only be observed using photography. Extending just beyond the visible region in the other direction from 700 nm and higher is the infrared region of light radiation. The range of infrared light close to the visible spectrum is also photographically reactive.
There are basically three common types of film: black and white, color negative and transparency. Film has varying degrees of sensitivity to the amount and intensity of light. These degrees of sensitivity are referred to as ASA. The higher the ASA number the “faster” the film. Faster film reacts quicker to light, therefore it requires less light for proper exposure. The drawback of using higher ASA film is that enlarged photos may appear grainy and less detailed.
Although slide film has accurate color rendition, it lacks “latitude.” Latitude in photography is the ability to produce a good picture from a negative that is slightly underexposed or slightly overexposed. These corrections can be to print film through adjustments in the print processing. Slide film is not designed for print processing and thus lacks latitude. This means that the exposure must be exact for the photo to turn out correctly. In addition, for use in trial situations, slides are more expensive to convert to enlargements than print film.
Since print film offers considerable latitude in exposure, it provides a definite advantage for those who are not expert photographers. Because documentation of evidence requires the reproduction to be as accurate as possible, color film is the best medium.
Yet in domestic violence photography, UV and IR techniques are often used to see images that our eyes cannot see. These techniques are useful because of the way our skin interacts differently with UV and IR light compared to visible light. For these techniques black and white film offers the best results.
There are two reasons for this. First, the top emulsion layer of all color film which is blue, contains UV blockers preventing the exposure of the bottom layers. Second, the blue layer that does react does not provide as much contrast as black and white film. In addition, there is no “color” in the UV and IR region so nothing is gained using color films.
It should also be noted that special IR film is needed for IR photography. Normal black and white film is not sensitive to the near IR region. IR film is sensitive from the IR region to the UV region and may be used for both techniques.
Polaroid Corporation has an active market in domestic abuse photography by utilizing their pack films and instant cameras. These systems work well when instant results are necessary. However, the color balance is not comparable to print film, and either duplicates or enlargements must be made by re-photographing the Polaroid picture with print film. Despite its shortcomings, the simplicity of the instant camera may be critical if the alternative equipment and necessary skills are not available.
Cameras and Lenses
For the photographic techniques illustrated in this article a 35 mm single lens reflex (SLR) camera is needed. SLR cameras are versatile because of interchangeable lens and filter adapters which are necessary for abuse photography.
To obtain adequate detail, close-up photography is essential for the techniques that will be outlined. The SLR camera incorporates a mirror and a prism that enables the subject to be viewed through the camera lens. This allows the photographer to document exactly what is framed by the viewfinder without “chopping off” the subject or getting out of focus.
35 MM point-and-shoot cameras will not work. The minimum focusing distance (approximately 3 feet) is not adequate to fill a frame. Built-in wide angle lens and the viewfinder optics used for framing and focusing are separate from the lens. With a point-and-shoot camera, the photographer may be able to focus the subject in the viewfinder, but the picture will be either out of focus of “chopped off” because the lens is not able to focus.
For domestic violence photography a shorter focal length is better. A f1.4 to f1.8 normal or macro lens is good enough to get close to the subject for detailed pictures. Most of the photographs taken in domestic violence photography will be taken at the minimum focusing distance to “fill the frame.”
For UV photography the lens must transmit light into the UV region. However, most lenses have been treated with a coating that blocks UV light. If money is not an issue then an expensive quartz lens may be purchased. On the other hand if money is a concern the alternative is to check the ability of a lens to transmit UV light. This is accomplished by performing an analysis to determine the percent transmittance of light less than 400 nm with a spectrophotometer. If the lens does not transmit light in this region of the spectrum it will not work for UV photography.
In photography controlling light is essential to obtain the proper exposure of film. This is achieved by manipulating the reciprocity law of photochemistry. The law states that exposure (E) is equal to the product of intensity (I) multiplied by the time (T). E=I x T
The shutter speed on a camera determines the amount of time the film is exposed. The settings on a given camera may range from 1 second to 1/1000 of a second. Proceeding from 1 second each step down reduces the time by one half. An example of shutter-scale markings would be as follows:
1, 2, 4, 8, 15, 30, 60, 125, 250, 500, 1000
Intensity is dependent on the maximum amount of light available and may be reduced by adjusting the aperture on the camera. The aperture is a diaphragm of metal leaves forming a nearly circular opening that the light has to pass through in order to reach the film. The range of aperture sizes are adjusted by turning a ring on the outside of the lens. The aperture settings (f-stops or f/numbers) usually consist of the following sequence: 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, … The smallest f/number is the largest opening, while the largest number is the smallest opening. For every consecutive increase in the f/number, the amount of light is decreased by half.
Because domestic violence photography is done indoors the light sources used have relatively low intensities compared to sunlight. Therefore the choice of film and the settings for the aperture and shutter speed need to be adjusted to allow enough light to reach the film while still being able to hold the camera. It is possible to “blur” a picture when holding a camera if the film and the shutter speed are too slow. This problem may be avoided by choosing a fast film such as 1600 ASA, in addition to setting the aperture shutter speed pairing based on the cameras built-in light meter. It is important that the camera has a built in light-meter, as photographing without one will be nearly impossible.
The light source is another variable that may need to be manipulated in order to obtain enough light for proper exposure. Because light waves spread out as they travel away form the source, the farther away the light source is from the subject the less light there is being focused on the subject.
The relationship between light intensity and distance is as follows: the light that falls on the subject is inversely proportional to the square of the distance. This relationship is known as the inverse square law. What this means to the photographer is that the intensity of light falling on the subject can be doubled by decreasing the distance from the source to the subject by half.
Photographing Injuries to the Skin
Penetration and reflection of light on the skin is a function of wavelength. Shorter wavelengths such as UV do not penetrate the skin very far before it is reflected back to the camera. Therefore a high resolution picture of the skin surface is possible. This works well for bite marks, cuts, scratches and scars. This is not a good technique to apply to bruises unless the blood accumulation is very close to the skin surface.
UV Photography can be accomplished with an ordinary 35mm SLR if the lens is capable of transmitting light somewhere between 300 nm to 400 nm. The easiest way to make that determination is to place the lens in a spectrophotometer and test it. Most clinical, university or forensic laboratories have one available. Manufacturers coat most lenses to prevent excess UV penetration. Excess UV will unbalance a color photograph with excess blue. There isn’t a common lens manufacturer that can be recommended. Some lenses will allow UV light transmission down to the 350 nm range and some will not. A simple test in the absence of a spectrophotometer is to photograph someone with freckles. The appearance of freckles in UV light is considerably enhanced compared to standard visible range light photography. No focus correction is necessary. Success in UV photography is also a function of light intensity (I) in the absence of the other wavelengths. To handhold photograph a living object requires a high intensity source such as an Omnichrome 1000 or Omnichrome FLS 5000 and a dark room. Photography with small handheld UV sources is possible, but standardization of source-to-target and lens-to target distance are critical. The following features are a good starting point for UV photography:
- 35mm SLR with fl.4 or 1.8 normal lens
- 3200 ASA Black and White film
- UV source
- Room without windows to turn out the room lights
- Measuring scale-to-place near injuries
If there is a need for macro photography, avoid complex lenses and use extension tubes. Proper light metering with a through-the-lens light meter is close enough that bracketing your shots will lead to a quality photograph.
Visible Light Region
After an assault the victims’ injuries may be photographed any time within the next two to five days. Visible light penetrates deeper into the skin than UV light and is sufficient to document most bruises.
The addition of special wavelength sources and special filters can improve the visualization of the injuries by enhancing the blue color and improving the contrast against the normal skin tones.
The equipment of choice again is a 35mm SLR with a fast lens. No special wavelength considerations are necessary. Most of the shots are at the minimum focusing position on the lens and available light as opposed to flash. If the room has florescent lights be sure to use a correction filter such as the Cokin A.036. Standard documentation with available light is usually followed with special wavelength photography that is sometimes called “Alternate light photography” (ALP). The Omnichrome 1000 or the Omnichrome FLS 5000 have positions for 450 and 485 nm that emit a blue light that improves the visibility of bruises. High ASA films such as Kodak Gold 1600, Ektapress 1600 or Fujicolor Super HG 1600 are the films of choice. ALP in combination with an orange filter (Cokin A.002) requires a fast film for handheld photography.
Through-the-lens light metering is accurate with visible and ALP photography. Beware of using a white ruler or measuring tape in close-up pictures. The meter may take the light reading of the scale and the skin tones and injury will be too dark. This can be avoided by keeping the scales at the edge of the photo since most light meters are center weighted.
The crime victim should be accompanied by a Victim’s Assistant from the District Attorney’s office when being transported to the laboratory. A short interview is conducted to determine the location of the injuries and how the injuries occurred. Bruises are transfer patterns. The victim’s statements may be supported by placing fingers on the finger marks or blunt instruments over blunt injury bruises. If a weapon was used, be sure to bring it to the photos session whenever possible. Rough anatomical drawings and a standardized form are used to determine the time interval for each injury. Any scars or birthmarks are also noted.
After the interview the photographic procedure is as follows:
- Place an 18% gray scale against the arm of the victim to aid the developer in assigning the proper skin tones. Also identify the victim and include a case number for reference.
- Starting with visible light photo techniques, photograph the upper half of the victim for identification purposes.
- Photograph the general area or appendage where the injury occurs.
- Adjust the lens to the minimum focusing distance and photograph the injury. (Small injuries may require the use of extension tubes). Place a scale in the photos.
- Look for patterns in the bruising. Re-photograph with suspect’s weapon adjacent to the bruise, then directly over the bruise. If the finger marks are on one side, look for the thumb mark on the other side.
- Repeat the sequence with the ALP source and appropriate filters with the room lights out.
- If UV photography is a consideration, change to 3200 ASA black and white film and repeat the sequence with a UV source. Bracket these shots extensively.
The methods discussed above have been employed for the last year in casework and are the result of extensive literature review and research on how to best represent the victims of domestic violence. All cases are by appointment to contain the labor costs. The methods have found application not only to spousal abuse or child abuse, but also to rape victims and homicide victims prior to autopsy and homicide suspects to document their injuries or lack of injuries. These techniques could be applied to elder abuse and fatal traffic accidents to identify the driver.
Most of the domestic abuse cases that have been photographed in the laboratory have been prosecuted or resolved in a positive manner. This is a direct reversal to the national statistics associated with domestic violence. One surprise that has occurred is the upgrade of charges when ligature marks can be documented. In one recent case the photography resulted in the grand jury upgrading the charges from Assault IV to Attempted Murder. The case went to trial and the suspect was found guilty of Attempted Murder. Of course this is the exception as most cases end with the abuser pleading guilty and getting a diversion to counseling. If the photography is done properly the abuser has lost his leverage over the victim and the case may proceed without the victim’s testimony. After all, let’s look at the reality of the circumstance, “Mrs. Smith, is this you in the photograph?” or, “Mr. Smith, is this your wife?”
- The Practical Methodology of Forensic Photography David R Redsicker, Elsevier, New York, New York 1991
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