Digitally processing an image of a shoe impression in blood

Shoeprints are valuable crime scene exhibits because, given a reasonable-quality impression and a suspect shoe, the forensic investigator can correlate the impression with the shoe and pin down a suspect. In similarity to bloody fingerprints, a common practice with bloody shoeprints is that the crime scene investigator photographs the impressions at a 90° angle with a scale, develops them with amido Black, and then photographs again. In most cases, the post-development prints will feature better and more details that are usually sufficient to perform a comparison between the impression found at the crime scene and suspect's shoes. This study examined shoeprints in blood that had been collected in an apartment in northern Israel where two bodies were found. The floor tiles in the apartment had featured a colored design which in the post-development photographs of the shoeprints blended in with the blood on the floor. As a result, the shoeprint impression was partial and small details were masked. In the laboratory, we processed the pre-amido Black photograph in several steps designed to increase contrast. The result of this digital processing was a full shoeprint sufficiently clear to display randomly acquired characteristics of the sole and subsequently establish identification between the impression found at the crime scene and suspect's shoes. When chemical amplification is not sufficient, it is worth exploring other methods before proceeding with the comparison, as it is sometimes still possible to extract information from the same data using alternative methods in order to achieve a conclusive result.