A comparison of the length and width of static inked two-dimensional bare footprints found on a hard compared to a soft surface

Similarity quantification of bare footprint based on linear measurement and shape context contour combined score-based likelihood ratio evaluation

Bare footprints are a type of physical evidence that can be crucial for solving difficult cases. To assist with identification, we explored a similarity quantification method using 3062 bare footprints from 1391 volunteers. We used linear similarity to cover seven linear lengths and then calculated the contour similarity of the heel region, anterior margin, and toe region using the shape context. Discriminant analysis was applied to determine the weights of the linear and contour similarities. Linear similarity had a weight of 0.56 whereas contour similarity had a weight of 0.44. The similarity between the same source and non-matches bare footprints was significantly different, with a leave-one-out cross-validation accuracy of 98.8%. Using the constructed similarity model, we developed a score-based likelihood ratio model based on similarity scores. We applied this model to five representative test samples including different volunteers, six months apart bare footprints, dynamic walking and static bare footprints. This method eliminated the interference of motion states and allowed for accurate determination of the same source and non-matches test samples. Overall, we quantified the shape contour and established a similarity assessment system for bare footprints that can assist in evaluation and identification.

Ghosting phenomenon in static and dynamic footprints in India and the United States

Ghosting is the phenomenon that exists when a footprint has a lighter area around the tip of one or more toes or a shadow-like area at the back of the heel. To date, ghosting has been considered primarily a finding of dynamic (walking) footprints, rather than static (standing) footprints. The prevalence of ghosting in static footprints is unknown, and research on its presence in static and dynamic footprints from the same participant is sparse, as are studies on its occurrence in different geographic populations. This study is among the first to evaluate the occurrence of ghosting in the static and dynamic footprints from a particular individual with participants in two geographic populations. A combination of both inkless and ink footprint collection systems were used to obtain a total of 206 bare footprints from 103 adult participants from the United States and India. The data comprised 103 static and 103 dynamic footprints. Ghosting occurred significantly in static footprints, though less frequently than in dynamic footprints. Ghosting in static footprints was seen most often at the first toe, followed by the third and second respectively. This aspect appeared least at the heel. In dynamic footprints, it occurred most at the first toe, followed by the second and fourth toes, and then the third toe and the heel. The prevalence of ghosting in footprints from the United States and India differed in their locations, notably at the first and second toes in the static footprints and at the heel in the dynamic footprints.