Automatic identification of firing pin impressions based on the Congruent Matching Cell (CMC) method

Firing pin impression is a kind of important physical evidence for forensic investigations. However, due to the small effective area and complex topography, the identifications are still rest on manual evaluations, and the studies on automatic recognition and identification are rare. In this paper, an automatic identification solution for three-dimensional (3D) firing pin impressions is proposed using a newly developed isotropic areal spline filter to extract the individual characteristics from the high order form of firing pin impressions, and an improved algorithm of the Congruent Matching Cells (CMC) method based on the valid data based normalized cross-correlation (VDNCC) to perform the identifications. This method is tested using 4,005 correlations from 90 cartridge cases. The results indicate that the proposed method is effective for identifications of firing pin impressions. The validation tests also show that the characteristics of the ammunitions may seriously affect the identifications and should be tested before performing test fires.