The infrared lighting system for the efficient photography of the pretreated fingerprint

Abstract

Detecting fingerprints at a crime scene is one of the most crucial factors in the preliminary investigation, and represents a considerable part of any crime scene investigation. Fingerprints obtained at a crime scene are processed into digital data, which can be used with an AFIS (Automated Fingerprint Identification System) and used to identify persons of interest. Therefore, it is necessary to promptly record fingerprints at a crime scene. This research offers an infrared photographic system that can efficiently record the fingerprints at a crime scene. We conducted an experiment, using IR bandwidth filters of 10 * 15 nm and tungsten illumination of color charts, recorded with an IR capable camera, which indicated that this configuration can record multi-colored backgrounds as a single bright color. The purpose of this experiment is to find the optimum infrared wavelength that can remove the complex multi-colored backgrounds of the fingerprint on the surface. In addition, we made an infrared lighting system with the optimum infrared wavelength after considering both the infrared capacity range of an adapted digital camera and the result of the experiment. The IR lighting system uses an LED (light emitting diode), which has its peak at 940 nm, as the light source, and is designed to be attached to the front of a lens. In addition, this system can be easily used by anyone for infrared shooting when used with a digital camera that supports a live-view mode. In a second experiment, pretreated fingerprint samples are photographed in a darkroom using the adapted digital camera and the infrared light system proposed in this research. Since carbon-based black fingerprint powder cannot be illuminated to appear bright, the method of illumination and image recording, combined with the application of black powder to a fingerprint, results in the recording of an image where the fingerprint is dark with a bright background. The fingerprint can be isolated from the multi-colored background that normally make the fingerprint difficult to record. We hope that it will be a method that can supplement the loss from fingerprint 'lifting' techniques, which are the mostly commonly used detection techniques at crime scenes today.