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Automated analysis and comparison of striated toolmarks



Michael Heizmann
Fernando Puente León


Proceedings of the Fourth European Meeting for Shoeprint/Toolmark Examiners (SPTM 2001), H. Katterwe, A. Körschgen (eds.), 2001.



Current matching methods for striated toolmarks are often unable to provide the turnaround times and success rates that law enforcement demands. To approach this challenge, we present in this paper a new image processing system that enables an automated extraction and matching of such patterns. For this purpose, a signal model is proposed that allows a suitable description of the interesting characteristics of striated toolmarks. To provide for a high image quality, several images of the same surface area are recorded with systematically varying object distances and lighting constellations. The images obtained are then combined to an improved result by means of appropriate sensor fusion techniques.
Based upon the signal model, the signal of interest is concentrated, and a compact representation of the grooves is obtained. To enable an efficient description of the relevant features even in the cases of deformed surfaces or curved striation marks, a straightening of the grooves is performed before. Following, a meaningful signature describing the information of interest is extracted using the whole length of the grooves. Finally, by comparing the extracted signature to another one, a metric measure is obtained. Thus, an objective evaluation of similarity of the toolmarks is enabled.
The performance of the proposed strategy is demonstrated with a database of real striation patterns. After having achieved successful matching results with firearm bullets, we present promising results for the more complicated task of comparing curved toolmarks.