Individual and collective identification in contemporary forensics

It has long been understood that individual and collective identification are inexorably intertwined. This convergence is not limited to genetics. This paper discusses the convergence of individual and collective identification in a comparative analysis of three other forensic areas: fingerprint analysis, microscopic hair comparison, and microbiome forensics. In all three case studies, we see purportedly individualizing technologies reverting, in a sense, to collective identification. Presumably, this has much to do with the perceived utility of collective identification. When knowing precisely who is the donor of a trace is not possible, or not useful, then knowing that the donor is ‘white,’ or ‘black,’ or ‘Middle Eastern’ begins to seem somehow useful. In each case, we also see that these collective identifications are ultimately founded on crude and broad, seemingly ‘commonsensical’ or ‘social,’ racial categories. These categories, meanwhile, are based on a less-than-fully-transparent combination of self-identification or official ascription. These suspect data are then transformed into seemingly persuasive scientific claims about the genetic attributes of this or that ‘race,’ ‘ethnicity,’ or ‘ancestry.’ Through this comparison the paper will explore how the individual and the collective are ‘done’ differently and similarly in different forensic disciplines

Method for estimating potential recognition capacity of texture-based biometrics

When adopting an image-based biometric system, an important factor for consideration is its potential recognition capacity, since it not only defines the potential number of individuals likely to be identifiable, but also serves as a useful figure-of-merit for performance. Based on block transform coding commonly used for image compression, this study presents a method to enable coarse estimation of potential recognition capacity for texture-based biometrics. Essentially, each image block is treated as a constituent biometric component, and image texture contained in each block is binary coded to represent the corresponding texture class. The statistical variability among the binary values assigned to corresponding blocks is then exploited for estimation of potential recognition capacity. In particular, methodologies are proposed to determine appropriate image partition based on separation between texture classes and informativeness of an image block based on statistical randomness. By applying the proposed method to a commercial fingerprint system and a bespoke hand vein system, the potential recognition capacity is estimated to around 10^36 for a fingerprint area of 25  mm^2 which is in good agreement with the estimates reported, and around 10^15 for a hand vein area of 2268  mm^2 which has not been reported before

The Individualization Fallacy in Forensic Science Evidence

Forensic identification science involves two fundamental steps. The first step is to compare a questioned item of evidence to an exemplar from a known source and judge whether they appear so alike that they can be said to match. The second step is to assess the meaning of that reported match: What is the probability that the questioned and the known originated from the same source? Different risks of error are present at each step. The risk of error in the first step is that a reported match between a questioned and a known sample might not really match. Even if the method used to compare questioned and known samples were flawless, an error could occur if, for example, one of the samples had been mislabeled or mixed up with a different sample. The risk of error associated with the second step is that, while accurate, the reported match may have arisen through coincidence and not because the samples share a common source. The risks of error at both steps affect the ultimate inferences that can be drawn about the identification evidence in a case. Both risks are subjects of far too little research. As to the first step, existing standards and procedures do not provide sufficient protection from erroneous conclusions that two marks are indistinguishably alike-that is, that they match when in fact they differ. Few, if any, criminalistics subfields have objective standards for deciding whether two patterns match