Although this approach produces images of the contact regions in shoe prints that are of the required quality, the entire process is time consuming and can be costly in terms of the consumables (e.g. The resulting shoe prints are then typically scanned to digital format using flat-bed scanners 1, 2, 3. This approach is very similar to that used during the retrieval of fingerprints. Previous studies have used fairly simple approaches based on commercially available footwear impression kits, where an ink pad (or reservoir of fluid), is used in conjunction with special sensitised paper to develop an image. It is also possible to compare images of shoeprints taken in custody, to marks that are found at crime scenes.Ī key component in the process of forensic image comparison and analysis involves some method of collecting images of shoe prints from suspects. The function of this database is very similar to that of the national fingerprint databases that currently exist in a number of countries in that it allows forensic scientists and practitioners to compare images of shoe prints obtained from crime scenes with a bank of images of known shoe types. Although such wear patterns would not necessarily be able to identify a person as the perpetrator of a crime as readily as say fingerprint or DNA would, they could be used to link them (or at least their shoes) to a particular location–information that could be vital to law enforcement operatives.Ī national footwear database (NFD) containing images of common shoe types has been developed in the UK to try to aid the processing of images that have been retrieved from crime scenes. These authors showed that the wear patterns formed on identical sets of boots worn by US marines during a training exercise, exhibited highly individual wear patterns. An excellent example of this was observed in a study performed by Fruchtenicht et al. These wear patterns are specific to the person wearing the shoes and could in principle be used as a means of identification. A person’s gait determines how they distribute their weight when they walk and this results in different extents of mechanical wear being present at specific points on the soles of their shoes. So how then, can we hope to use images of footwear that have been retrieved from a crime scene to differentiate between similar shoe types and identify an individual? The answer lies in the individual nature of the wear patterns that are exhibited by shoes worn by different people. There are only a finite number of shoe types in circulation and only a small subset of these are found at crime scenes (this is particularly true in the UK). Imaging footwear marks and cross matching shoe types does not provide as clear an identification of an individual as say fingerprint or DNA evidence. Here we describe one such approach based upon frustrated total internal reflection imaging that can be used to acquire images of regions where shoes contact rigid surfaces. This is particularly true in the burgeoning field of forensic footwear analysis, where images of shoe prints are being used to link individuals to crime scenes. A consequence of this is that new, low-cost imaging technologies are required to simultaneously increase the quality and throughput of the processing of evidence. Ongoing changes in government policy, increasing crime rates and the reduction of forensic service budgets increasingly require that evidence be gathered and processed more rapidly and efficiently. However, despite recent advances in machine vision technology and image processing techniques (and contrary to the claims of popular fiction) forensic image retrieval is still widely being performed using outdated practices involving inkpads and paper. Forensic image retrieval and processing are vital tools in the fight against crime e.g.
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