Forensic discrimination of photocopy toners by FT-infrared reflectance spectroscopy

Because of the speed, simplicity, and accessibility of photocopying, forensic examiners are encountering photocopies as often as original questioned documents. We investigated the ability of FT-infrared microscopy coupled with pattern recognition methods to discriminate among copy toner samples from a variety of manufacturers. Infrared microscopy is a preferred method due to its non-destructive nature, however, visual comparison is difficult because the observer may not be able to fully utilize the fine structure of the complex patterns. Principal component analysis and canonical variate analysis were used to visualize clustering of samples and to assess the statistical validity of the observed differences. The results illustrate the potential for computer-assisted data interpretation to provide decisive forensic identification of questioned samples.