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Guideline for the Use of Infrared Radiation (IR) in Forensic Science

SWGDE 19-P-002-1.1

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Table of Contents

1. Purpose

The purpose of this document is to provide an understanding of how infrared radiation (IR) photography can be used to document and examine evidence. In this document, the use of the acronym “IR” will also apply to Near IR (IR).

2. Scope

This document provides a basic understanding of the principles of fluorescence and reflectance as they pertain to IR, the equipment needed for IR photography, its use when documenting and examining evidence, and procedures for capturing images. This covers an advanced photography technique and does not address basic principles of photography.

3. Limitations

  • Depending on the camera’s imaging sensor, Near IR (NIR) ~1100 nanometers (nm) may only be detected versus the full IR spectrum.
  • Not all substrates and surface materials will create contrast when exposed to IR.
  • Since the infrared (IR) spectrum does not contain color information, images captured in IR will display false colors and should be converted to black and white after capture.

4. Equipment

Please reference SWGDE 16-P-001-2.0 Photographic Equipment and Infrastructure Recommendations prior to implementation of new equipment or procedures.

  1. IR capable digital camera or system.
    1. A full-spectrum camera or a camera that has been professionally modified to allow for the capture of images in the IR spectrum.
      1. Full-spectrum cameras are sensitive to wavelengths of energy from ultraviolet (UV), visible, and IR.
      2. Professional modified cameras with an IR filter installed will often only be sensitive to IR. When using a professionally modified camera, you will need to select the filter conversion that best serves the agency’s needs.
      3. IR focuses at a different point than visible light and each lens may have a different focus shift. It is important to test the camera with the lens prior to use.
      4. A digital camera with “live view” is for viewing and focusing with an IR filter.
      5. For comparative analysis photography, a fixed focal length macro lens is recommended.
      6. For documentation photography, a variable focal length lens may be utilized; however, this may cause or create distortion of the image.
  2. Filters
    1. Visible band pass filter (if using a full-spectrum camera to capture natural light images).
    2. IR transmission filters (block visible light and allow IR to pass through).
  3. Variety of light sources
    1. Reflectance – Dedicated IR source or a light which emits in the IR spectrum (e.g., tungsten light bulb, detachable flash, floodlight, flashlight)
  4. Fluorescence
    1. Alternate light source (ALS) typically in the blue/green wavelengths (~450-550 nm)
  5. Remote shutter release
  6. Sturdy tripod or copy stand capable of various angles and positions
  7. Digital storage media
  8. Standardized scales of various sizes
  9. Appropriate Personal Protective Equipment (PPE)

5. Basic Principles Behind IR Photography

The visible portion of the electromagnetic spectrum (Figure 1) includes wavelengths of approximately 400-700 nm. IR is outside the visible spectrum of light. In general, the NIR range from 700 to 900 nanometers has the most practical application for forensic photography.

Figure 1. Electromagnetic Spectrum (Figure Credit: Google Creative Commons Licenses)

IR photography takes advantage of a camera sensor’s ability to capture wavelengths that are outside the visible spectrum. IR reflectance photography is a technique that captures IR energy. IR fluorescence photography captures fluorescence re-emitted by a subject that has been excited by a light source of a shorter wavelength, typically in the blue/green range (450-550 nm). In these techniques, subjects that reflect IR will appear lighter in appearance.

This technique is beneficial when an item of evidence and its background are the same tone under visible light but react differently to IR. Documentation of evidence, such as blood or gunshot residue on dark clothing, injuries or tattooing on skin, and questioned documents may benefit from the use of IR photography.

IR transmission filters are designed to allow IR wavelengths to pass through the camera lens to the sensor while blocking the visible light wavelengths. The filters allow for additional contrast to be created. Different filters are available to control which wavelengths are transmitted to the camera sensor.

Table 1 lists several IR filter manufacturers. This list is not inclusive of all possible filters or manufacturers.

Blocks Wavelengths Below Wratten Schott B+W Helio Hoya PECA
580nm
25
OG 590
90
1025/125
25A
716/721
600nm
29
RG 630
91
1029/129
723
645nm
70
RG 665
902
680nm
89b
RG 695
92
5695/569
R72
914
700nm
88
720nm
88a
RG 715
5715/571
912
740nm
87
RG 780
5780/578
904
790nm
87c
RG 830
93
5830/583
910
820nm
87b
RG 850
5850/585
RM90
908
880nm
87a
RG 1000
94
5100/510
RM100
906

Table 1. Examples of IR filter manufacturers (Table Credit: SWGDE)

6. Examples of IR Photography

6.1 Blood on fabric

Figure 2. Images of blood on fabric with visible light and various filters (Figure Credit: SWGDE)

6.2 Gunshot residue (GSR) on fabric

Figure 3. Images of gunshot residue on fabric produced with visible light (left) and reflected IR with filter (right) (Figure Credit: SWGDE)

6.3 Tattoos on the skin

Figure 4. Tattoo images using visible light (left) and reflected IR with filter (right) (Figure Credit: SWGDE)

6.4 Ink

Depending on the formulation, the ink will react differently to IR: some will fluoresce, some will reflect, and some will absorb.

Visible light
Reflected IR with 87 filter
IR fluorescence with 87 filter and ALS blue/green wavelengths (~450-550 nm)

Figure 5. Ink under visible light (top left), reflected IR (top right), and IR fluorescence (bottom) (Figure Credit: SWGDE).

Visible light
Reflected IR with 87C filter
IR fluorescence with 87 filter and ALS blue/green wavelengths (~540 nm)

Figure 6. Ink on paper under visible light (top left), reflected IR (top right), and IR fluorescence (bottom) (Figure Credit: SWGDE).

6.5 Bite mark(s)/bruising

IR penetrates the skin showing deeper bruising. However, it may not be the best technique to use if the bruising is superficial.

Figure 7. Bruising images under visible light (left) and reflected IR (right) (Figure Credit: SWGDE).

6.6 Fabrics/Textiles

The IR photography technique could be used to document clothing for possible comparison against an IR video image. Different fabrics, patterns and blends will absorb IR light in different ways depending on the manufacturing. (e.g., a black t-shirt could appear light gray under IR or logos/branding can look different or components completely lost during capture).

Figure 8. Fabric under visible light (left) and reflected IR (right) (Figure Credit: SWGDE).

7. Procedures for IR Photography

These procedures are written for a full-spectrum camera. If a dedicated IR converted camera (that only captures IR) is used, then skip steps 6 – 8.

It is suggested that the subject also be documented using visible light photography. If utilizing a preconfigured system, refer to the appropriate user manuals.

A camera with live view capabilities will allow the item/object being photographed to be observed and focused before capture because it will not be visible through the viewfinder.

7.1 Procedure for reflected IR photography

  1. Mount the camera to a tripod, copy stand, or another sturdy device
  2. Set the camera to the lowest ISO for the lighting conditions
  3. Set the camera to manual mode
  4. Set the file format to RAW
  5. Set the camera’s white balance to the color temperature of the visible light (Since IR images do not contain color information, no changes are necessary for the IR photos)
  6. Compose the subject so that it is perpendicular to the camera – place a scale and label on the same plane as the subject
  7. Apply even and direct lighting (do not diffuse) to the subject
  8. Place a visible bandpass filter on the camera and focus
  9. Meter for visible light, capture an image, review, and adjust as necessary
  10. Using the same light source, or another high in IR output, apply even illumination to
  11. Remove visible bandpass filter
  12. Place the IR filter on the camera and focus – for a non-calibrated lens, use either live view (if equipped) or adjust for maximum depth of field
  13. Capture an image, review, and adjust exposure settings as necessary

Use of different filters may be necessary to achieve the desired results.

7.2 Procedure for Fluorescence IR

  1. Mount the camera to a tripod, copy stand, or another sturdy device
  2. Set the camera to its lowest ISO for the lighting conditions
  3. Set the camera to manual mode
  4. Set the file format to RAW
  5. Set the camera’s white balance to the color temperature of the visible light (Since IR images do not contain color information, no changes are necessary for the IR photos)
  6. Compose the subject so that it is perpendicular to the camera – place a scale and label on the same plane as the subject
  7. Apply even and direct visible lighting to the subject
  8. Place a visible bandpass filter on the camera and focus
  9. Meter for visible light, capture an image, review, and adjust as necessary
  10. Remove the visible bandpass filter
  11. Replace the visible light with a light source of approximately 450nm to 550nm (blue/green). Do not diffuse.
  12. Place the IR filter on the camera and focus – for a non-calibrated lens use either live view (if equipped) or adjust for maximum depth of field
  13. For best results, it is recommended to capture the image in a dark environment
  14. Capture an image, review, and adjust exposure settings as necessary

Use of different filters may be necessary to achieve the desired results for the subject.

8. Additional Resources

9. History

Revision Issue Date History
1.0 DRAFT
9/19/2019
Initial draft created and voted by SWGDE for release as a Draft for Public Comment
1.0 DRAFT
9/19/2019
Formatting and technical edit performed for release as a Draft for Public Comment
1.0
9/17/2020
Voted for release as Final Approved Document.
1.1 DRAFT
1/12/2026
Five-year review performed. Updated to include figure/table credits and formatting into new template. No substantive changes made to technical content. Moved forward for SWGDE membership vote to release as a Final Approved Document.
1.1
2/19/2026
SWGDE voted to approve as Final Approved Document.
1.1
3/9/2026
Formatted for release as Final Approved Document.

Version 1.1 (3/19/2026)

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