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Guidelines for Digital Imaging of Footwear and Tire Impressions

17-P-003-2.0

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Table of Contents

1. Purpose

The purpose of this document is to offer guidelines on how to capture images of footwear and tire impressions for the purpose of conducting comparative analysis.

2. Equipment

  • Digital single-lens reflex (DSLR) or Mirrorless Interchangeable Lens Camera (MILC)
  • Detachable flash with remote capabilities
  • Fixed focal length lenses (see Section 3, Considerations)
  • Remote shutter release
  • Sturdy tripod mount capable of various angles and positions
  • Variety of light sources (e.g. floodlights, flashlights, Alternate Light Source [ALS])
  • Level/angle finder
  • Flat rigid scales
  • Tape Measure (for tire impression)
  • Reflector
  • Diffuser or shade to control ambient light

3. Considerations

It is important to minimize distortion when capturing images for comparative analysis. Professional quality fixed focal length (prime) lenses have significantly less distortion than variable focal length (zoom) lenses. Additionally, a prime lens with a focal length of 50mm or higher is recommended. If a prime lens is not available, set the zoom lens to a focal length of 50mm or higher. Never use a wide-angle lens to photograph impressions.

Figures 1 and 2 were both taken with a zoom lens and demonstrate this point. In Figure 1, the focal length was set to 50mm. In Figure 2, the focal length was set to a wide angle. Notice the distortion of the entire image, especially evident in the ruler.

Figure 1. 50mm focal length (Photo Credit: SWGDE)
Figure 2. Wide angle focal length (Photo Credit: SWGDE)

The following procedure may be used to test equipment for distortion:

  1. Mount camera on a tripod or copy stand.
  2. Use a level to ensure that the camera’s sensor plane is parallel to the target.
  3. Fill the frame with a sheet of graph paper or target grid.
  4. Square the lines in the viewfinder.
  5. Take a picture.
  6. Repeat the procedure at each focal length.
  7. Using the resulting images, identify the focal length(s) where no visible distortion occurs.

Figures 3, 4, and 5 show types of image distortion.

                                                        Figure 3. Minimal Distortion                                            Figure 4. Barrel Distortion                                                                                                                   (Image Credit: SWGDE)                                                   (Image Credit: SWGDE)

Figure 5. Pincushion Distortion

  (Image Credit: SWGDE)

4. Procedure

A typical standard operating procedure for Impression Photography should include the following:

  1. Locate impressions to be photographed.
  2. Take overall and medium range photographs of the location of the impressions.
  3. Mount the camera on a tripod with the sensor plane parallel to the impression.
  4. Set the camera to a file format with lossless or no compression (i.e. RAW or TIFF) and the highest resolution available.
  5. Set the aperture to optimize depth of field (e.g. generally two stops below the largest f-stop or smallest aperture opening to maintain image quality).
  6. Place a scale on the same plane or the furthest depth of the impression, then focus on the bottom of the impression
  7. Fill the frame with the entire impression. See Figures 6 and 7 for examples of correct and incorrect orientations.
Figure 6. Correct Orientation (Image Credit: SWGDE)
Figure 7. Incorrect Orientation (Image Credit: SWGDE)
  1. For each impression, take at least one photograph under ambient light, then take photographs using oblique lighting from various angles, including the four cardinal points (see Figure 8). If the ambient light is too strong, shade the impression to control the light more effectively with the flash.

Figure 8. Cardinal Point (Image Credit: SWGDE)

  1. FOOTWEAR: Separate close-up images of the heel and toe box area may be taken if they contain additional detail. Each image should contain an identifier and scale.
  2. TIRES: Due to their length, photographing tire impressions may present a unique challenge
    1. For continuity and orientation purposes, a tape measure should be positioned flat and extended along the side of the entire length of the impression. This overall scale should remain in place for all the photographs.
    2. Take multiple overlapping photographs of the impression to capture at least one full rotation of the tire following the steps outlined in 4.7 through 4.9.
    3. Each image should contain an identifying marker and scale in addition to the tape measure.
  3. If the impression is processed (e.g. with fingerprint powder or chemicals), re- photograph after each process with identifying marker and scale

5. Additional Resources

Academy Standards Board (ASB). Best Practice Recommendation for Photographic Documentation of Footwear and Tire Impression Evidence, ANSI/ASB Standard 050-21, ANSI/ASB, 2021.

6. History

Revision Issue Date Section History
1.0 Draft
8/24/2017
All
Initial draft created and SWGDE voted to release as a Draft for Public Comment.
1.0 Draft
9/25/2012
All
Formatted and technical edit performed for release as a Draft for Public Comment.
1.0 Draft
1/11/2018
3.1
Updates made in response to public comments. Voted by SWGDE for release as an Approved document.
1.0
4/25/2018
—
Formatted and published as Approved Version 1.0.
2.0 Draft
6/14/2023
—
Full re-write on v1.0. Submitted as draft for review. SWGDE voted to release as a Draft for Public Comment.
2.0 Draft
8/2/2023
—
Formatted for release as a Draft for Public Comment.
2.0 Draft
5/20/2024
—
SWGDE voted to approve as a Final Approved Document.
2.0
5/20/2025
—
Added ANSI/ASB additional resource.
2.0
8/1/2025
—
Formatted for release as a Final Approved Document.

Version: 2.0 (8/1/2025)

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