Crime scene photography using off-the-shelf gear: Part 3
CSI photographers must know how to properly document the scene by choosing appropriate vantage points for overall, mid-range, close-up and macro photos
In part one of this three-part series, I covered why color and accuracy of photos taken at a crime scene are important and how differences in lighting can change the color of evidence.
In part two, I discussed the types of lenses, lighting and color balance required to achieve the most accurate representation of in situ evidence.
This final installment reviews overall, mid-range and close-up photography.
Overall, mid-range, close-up
According to the FBI Academy’s document mentioned in part one, different "range" photographs usually can be categorized as:
- Focusing on the "location" of the crime;
- Concentrating on the "nature" of the crime;
- Centering on the "results" of the crime;
- Featuring the "physical" evidence existing at the scene;
- Focusing on "follow-up" activity not directly occurring at the immediate scene.
Overall photos give an idea of the entire crime scene – exactly where the scene is (and conversely where the scene isn’t), and shows all boundaries of the scene.
Photos should be overlapping and should be taken from the outside in and the inside out and even overhead if applicable, covering all areas of the scene. References can be compass points, walls, corners or other easily recognizable landmarks and many cameras automatically can capture GPS location. Evidence and their spatial relationships may be seen but that is not the key point of these photographs.
While it is important to have consistent lighting, capturing quick and dirty overlapping 360-degree photos with a color-checker card in view before anyone does a walk though can let investigators know if the scene has been altered in any way as evidence is identified and further photos are taken. We named several types of lenses and their use in part two. Two of them, wide-angle and anamorphic lenses, will make scene capture easier as you can see in Figure 1.
Many smartphones can take panoramic photos by standing in one place and rotating your body, but photos taken this way will be distorted with square angles and straight lines turning into something out of a cartoon. Even though the objective is to capture what is and is not present before the scene is contaminated, significant distortion from a panoramic photo may be an issue.
See Figure 2 and note how an anamorphic lens can capture an image about 75% as wide as the iPhone’s built-in panorama function but with much less distortion (and lower overall resolution as well).
If you want the exact parameters of where a photo was taken, the iOS Theodolite app uses the iPhone’s on-board compass and tilt sensors to create a virtual reality viewfinder that combines a compass, two-axis inclinometer, rangefinder, GPS, map, nav calculator, and geo-overlay photo/movie camera. This app not only documents your exact location but also the direction the camera is facing along with how many degrees up or down from level it is pointed, further aiding crime scene reconstruction later in the process.
For our crime scene, we took wide-angle vertical overview photos facing approximately east and west and after placing evidence markers we took a Theodolite photo for more exact information. See Figures 3, 4, and 5 below.
Mid-range photographs move closer to the evidence and should be taken twice, once before evidence markers and color calibration tools are placed and then afterward.
Like a movie’s establishing shot, mid-range photos move the viewer from an “outsider looking in” to “you are there.” Evidence is shown in context with the surroundings, typically by showing a single item or related items in relation to a larger fixed object. Done correctly, this technique will show proper context, perspective, and scale. It also will show the precise position of each item of evidence.
Placing markers before photographs are taken could hide unnoticed evidence underneath as well as disturb the scene. Taking additional photographs after marker placement allows for more accurate sizing and cataloging.
If multiple agency staffers are available, have at least a second pair of eyes verify that all evidence is marked. You don’t want to look at photos back at the office and realize that you missed marking and photographing a piece of evidence.
Remember to record the locations of evidence, evidence markers and photos in your graph paper notebook. See Figures 6, 6a, 7 and 8.
Close-up photographs are designed to show every detail of the evidence and the entire object must be in focus, which may involve using a macro lens and small f stop for a deep depth of field.
Photographs taken in situ should use calibrated light with the camera oriented parallel to the surface being photographed and with the item filling the frame for the best resolution. Each photograph usually is taken twice: once without disturbing the evidence in any way and another with a measurement tool, such as a bureau reference scale or an evidence marker with a scale.
A color calibration target should be included if possible. Note the difference in the color of the concrete between figure 9, which is not color balanced and shows the concrete as white and figure 10 which is color balanced and shows the concrete as yellowish.
With markers carefully placed, now is the time to zoom in on your evidence. While the first photographs should be taken locally before moving an item, more detailed photographs must show all sides of the item, including any markings, defects, or other identifying features. This might require photos to be taken under studio conditions in a lightbox, which offers diffuse, calibrated shadowless light.
Figure 11 shows the same three pieces (or four pieces if you count the rubber band) of evidence in Figure 9 but with markers and a compass in place. The numbers on the markers allow for bagged evidence to be tied to specific photographs and descriptions in your notebook.
Figure 12 is taken with a 10x macro lens and is sharply focused to show every detail. How do we know which piece of evidence this is? Either from your notebook log or by taking a photo of the evidence marker just before you take the macro photo. Depending on the focusing distance of your macro lens, the use of notebooks or short tabletop tripods can hold small lights and stabilize your camera or smartphone.
Chain of custody
Many smartphones and cameras can store metadata with every photograph including what was used to take the photo, time, date, GPS location and exposure information. This should be enabled whenever possible so that it can be queried later on if necessary.
A documented chain of custody for every photograph taken will help prevent unauthorized modification or loss. As soon as possible, untouched photographs should be archived, perhaps to a write-once CD/DVD or to an encrypted flash drive and secured. Copies can be modified for sharpening or color balance and if there is any question as to their accuracy, they can be compared to the unmodified originals.
Consistent, balanced, accurate lighting is important for CSI photography. The use of high-CRI lights, low-distortion lenses and a calibrated color workflow throughout can help ensure that evidence is properly presented at all phases of the investigation and trial.
CSI photographers need to be aware of how to properly document the scene by choosing appropriate vantage points for overall, mid-range, close-up and macro photos. The use of evidence markers and bureau scales can help investigators understand the location and size of discovered evidence. A second or third pair of eyes can help ensure that evidence is not overlooked or left unmarked.
A notebook should be used to document every photograph taken – when, where and in what direction.