DECEMBER 31--Traditionally, collecting fingerprints requires dusting objects with powder to make the fingerprint visible, transferring an impression of the image to sticky tape, and then transferring the image onto clear sheets. These images are then compared with the legal agency's database of criminals' fingerprints. However, if fingerprints are collected from three-dimensional surfaces, fingerprint impressions will contain out-of-focus areas that may make it difficult to identify identification features such as whorls. To capture such images accurately requires that a number of photographs be taken and manually overlaid to produce a flat image of the fingerprint. Such methods are, however, laborious and time-consuming.

Therefore, the Wiltshire Police Fingerprint Laboratory (Devizes, Wiltshire, England) has installed a digital imaging system that captures fingerprint images from three-dimensional objects without removing or copying the images. Software is used to automatically overlay the fingerprint images to form one complete detailed image.

To visualize fingerprints, the laboratory uses high-intensity light sources to make fingerprint impressions fluoresce and, if necessary, backlights them to get the optimum photographic conditions. Fingerprint impressions are then digitally photographed using a DCS-121 digital workstation from Mason Vactron (Evesham, Worcestershire, England) either at the crime scene or in the laboratory.

After image capture, the workstation produces a digital negative that automatically flags any alterations made to it, prints out hard copies of black fingerprints on a white background, makes working digital copies of the validated digital negative fingerprint image, and stores the original as bmp or TIFF files. Digital fingerprint files are then processed by Auto-Montage software from Syncroscopy (Cambridge, England) to scan the image. The workstation then combine the most in-focus regions from a series of partially focused fingerprint images taken at different focal lengths and automatically produces a completely focused final image that can be used for identification purposes.

For more on this, see Vision Systems Design, January 2002.

Mon Dec 31 09:54:00 CST 2001