Special Lighting Techniques

Latent impressions can be found on a wide variety of surfaces and substrates, which can increase the level of complexity (difficulty) of digitally photographing the evidence.  For example, processing physical evidence with black powder can produce latent impressions with good “visible” detail that can be photographed without special lighting techniques.

Latent impressions (both latent prints and footwear) in soft substances (such as wax, putty, clay, adhesive tape, grease, or dust) require the use of oblique lighting at a low angle. This technique creates small shadows to visualize and photograph the impression.

Fingerprints on porous surfaces (textured wall coverings, wood, brick, etc.) typically require about a 90–degree lighting angle to avoid creating shadows from the surface texture.  Improper lighting can create shadows that will interfere with visualizing and photographing the impression.

Latent impressions developed on glass (windows, drinking glasses, etc.) can be photographed by placing a white card behind the glass and using a low oblique angle of light. They can also be photographed by using transmitted (back) lighting by positioning a diffused light source behind the glass.