Assessing some low- and no-cost image processing software for gunshot residue pattern analysis

The need for more accessible provision of forensic science services for resource-limited environments is increasingly being recognised. This prompted this assessment of low- or no-cost pattern analysis software for gunshot residue (GSR) images. Interpreting the spread of deposited GSR particles on surfaces is performed during ballistic reconstructions, particularly for close-range shootings. Such reconstructions rely on the correlation between GSR particle density and muzzle-to-target distance, which necessitates detection and interpretation of particle data from visualised GSR patterns. There are multiple digital imaging approaches for visualising GSR patterns, including traditional and infrared photography, fluorescence imaging, and imaging of chemical transfer patterns, each producing an output with different characteristics requiring analysis. Here, a selection of common open-source and free-to-use scientific software and plug-ins were applied to identify and analyse GSR patterns that had been documented using different imaging methods (infrared, fluorescence, and chemical nitrite development). The primary software used was 'Fiji'; an upgrade of ImageJ with expanded functionality, coupled with plug-ins for spot counting and colour deconvolution. Next, the feasibility of performing statistical analysis on the collected datasets was demonstrated using software 'R', wherein the pattern's centroid and region of interest parameters were measured as a basis for comparisons. Together, these tools may assist ballistic reconstructions involving interpreting images of GSR patterns, as well as when conducting research or validation of new or established GSR development techniques, in both well-resourced and resource-limited environments.