NCJ Number
143867
Journal
Journal of Forensic Identification Volume: 43 Issue: 4 Dated: (July/August 1993) Pages: 368-377
Date Published
1993
Length
10 pages
Annotation
This article describes the methodology and results of a test that shows the effectiveness of using time-resolved photography to enhance the image quality of fingerprints on fluorescent backgrounds.
Abstract
When the background for fingerprints fluoresces at wavelengths not blocked by the camera filter, the fingerprint image is obscure. The technique of time-resolved photography separates the desired signal from the background noise in the time dimension rather than in the wavelength dimension. If the fluorescence from the stained fingerprint is relatively long-lived, a well-chosen time delay between the actual excitation of the entire substrate and the observation of the continued fluorescence of the fingerprint will discriminate against an interfering fluorescent background. The delay must be sufficiently long to allow the background noise to decay, but short enough to allow for the recording of the fingerprint signal. This article reports on the success of time-resolved photography in producing clear fingerprint images from a glossy magazine cover and a soft- drink can. The test used the Kronem Systems TRP100 apparatus, which consists of filtered Xenon flash lamps and a Polaroid camera back gated by a spinning chopper wheel. The results show that a simple, inexpensive mechanical chopping system, rather than an electronic gating system, can be used if sufficiently long-lived chemicals can be made to react with the fingerprints. This test used a europium- containing chemical as the fingerprint powder. The author offers suggestions for future tests that can lead to even better image quality from fluorescent backgrounds. 3 figures and 12 references