Here we break down essential forensic photography techniques and terms you should know about.
Investigators and witnesses can describe crime scenes, sometimes in great detail. However, photographs can better tell the story with objectivity. They freeze time and leave a permanent record of the scene. Despite its advantages, photography remains the least understood and least developed skill for arson and crime scene investigators.
To help you teach future crime scene investigators (or to brush up on your own skills), we’ve assembled essential forensic photography methods, described photography terms every crime scene photographer should know, and provided a fingerprint distortion activity to hone photography skills.
Methods
Evidence at a crime scene should first be captured as discovered with no additional elements and juxtaposed to scale to indicate the size of the evidence photographed and its location relative to other evidence and landmarks.
Photographs should then be taken that include three elements:
- The subject
- A scale
- A reference object
The subject of the photograph should be the main object of the photograph and always be in focus. Photo evidence scales provide measurements for scaling the size of the object photographed in addition to other elements helpful for photography. The two or three crosshair circles on a scale are useful in compensating for distortion resulting from oblique camera angles, and alternating black and white bars aid in measurement of grossly over- or under-exposed photographs. A reference object is an object in the photograph whose measurements are known and recorded, such as an evidence number marker or scale.
To make sure your crime scene photographs are correctly taken, consider these additions to your crime scene documentation supplies:
Use these 6″ (15-mm) white vinyl scales from Sirchie® for precise measurement when photographing evidence. The scales are 0.02″ thick and are calibrated in both inches and millimeters with crosshairs at each end.
This reversible scale is primarily intended for footwear and tire track impression comparisons. It also is excellent for verifying perspective distortion. One side is black text on a white background; other side is white text on a black background.
Mark items of interest and measure them at the same time using the metric scale on this 2-in-1 device from Sirchie®. The plastic A-frame markers, numbered 1 to 20, are bright yellow with bold black lettering and have a 4.5-cm metric scale printed on the base.
Documentation is a core component of evidence collection and photography is no exception. Responding officers must maintain a photograph log whenever photographic documentation is taken. The log should contain the date and time of the photograph, subject matter, and relevant addition notes. These logs should be maintained within a case file or incident report as part of the examination record and are discoverable material at a trial.
Record the evidence in a format acceptable in most jurisdictions. Designed by the experts at Sirchie®, you can use this template to document blood spatters, bullet holes, tool marks, and many other kinds of physical evidence. Template is die-cut and features a preprinted scale, information blanks, and a 10 x 10-cm evidence area.
This standard format evidence label from Sirchie® has red lettering printed on white tape. It provides an authentic experience labeling and cataloging evidence for forensic activities. Label size, 1-1/2 x 3″. Dispenser box holds a roll of 100 labels.
Five photography terms every crime scene photographer should know
First, your goal as an investigator is to capture a crisp, clean image with as much detail as possible. To do that, you’ll need to take the camera out of auto and set it to manual mode.
Aperture
This is the size of the opening of the lens. It is expressed in f-numbers or f-stops (as in f/5.6). Smaller apertures let less light in and have a higher f-stop. Larger apertures (f/2.8—f/5.6) will allow more light into the camera, but the resulting photos will have a shallow depth of field (more on that later). Typically, you want to start with an aperture setting of f/8 to produce photos that are crisp from foreground to background.
Shutter speed
A slower shutter speed will leave the shutter open longer and let in more light. A faster shutter speed lets in less light. A good rule of thumb is to take a picture using a shutter speed that is faster than the fastest thing in your scene. Additionally, cameras should be mounted on tripods, so if you set a long shutter speed, the image won’t be blurry because your hand or other elements caused the camera to shake.
ISO
The ISO is the sensitivity setting for the camera sensor. The higher the ISO, the more sensitive the camera sensor is to light. A higher ISO also diminishes the quality of your image, and it will become “grainy” or “noisy.” For arson and crime scene photographs, we want the ISO set at the lower end (100, 200, 400, 800).
Depth of field
The depth of field (DOF) is how much of the foreground to the background is in focus. A large DOF is best for arson and crime scene photography because it makes everything crisp. A good tip to remember: a small aperture setting, such as f/22, will produce photos with a large depth of field, while larger apertures like f/2.8 will produce photos with a shallow depth of field.
Painting with light
This technique is especially useful for arson investigators, because their scenes are typically dark with no natural light and often no other light sources available. To paint with light, use your flash or flashlight to shine light all around the scene so you can capture important details. You need a good tripod, your camera set in manual, and your camera flash or a flashlight.
To paint with light:
- Always mount the camera on a tripod. Open the shutter for a long exposure. This will let in more light.
- Choose a small aperture that will maximize your DOF.
- Consider raising the ISO a little, making the camera sensor more sensitive to light.
- Walk around the scene and use your flashlight or multiple flashes to paint the scene with light from all angles to capture more details.
Fingerprint distortion activity
In this extension activity, you will examine the importance of the camera angle and the distortion of fingerprint evidence.
Materials
- Developed Fingerprint
- Digital Camera or Cell Phone Camera
- Piece of Card Stock or Index Card (4 x 6″)
- Plastic Protractor
- Clear Tape
- Ring Stand
- Ring Stand Clamp
Procedure
- Secure the developed fingerprint to the card stock or index card using a small piece of tape.
- Tape only the bottom edge of the card to the table. This serves as a hinge.
- Set up the ring stand and clamp so the camera or phone is 8 to 10 inches from the flat fingerprint.
- Take a picture of the fingerprint. The fingerprint should be 90 degrees, or perpendicular, to the camera lens. Do not move the camera setup.
- Use the protractor to raise the top edge of the card by 15 degrees. Take a picture.
- Continue to raise the card in 15-degree increments and to take a picture until the card is upright–0 degrees, or in line with the camera.
- Compare each picture with the original fingerprint. Which image looks the best?
Discussion
Assume the role of a forensics expert testifying in a murder case and explain to the jury why photographing fingerprints is a critical step in gathering evidence.
Recommended supplies for the fingerprint distortion activity:
Professional kit contains all materials needed to teach FBI fingerprint searching techniques. Students get hands-on experience in fingerprint detection. With instructions and carrying case.
This kit is loaded with the latest in fluorescent fingerprint technology, including a MicroBlue light source, bottles of PowderJet, fiber duster brushes, and fingerprint lifters.
