Quantifying the uniqueness of fingerprints from the same source

Abstract

In 2009, the NAS published a report that was critical to forensic science, including the fingerprinting discipline. In particular, the report highlighted the fact that many of the claims made by LPEs are not backed up by scientific research. One of those claims is that if two fingerprints can be overlaid perfectly then one must be a copy. This study aims to provide research that will support or refute this claim and satisfy the demands of the NAS report. Additionally, this study was performed, in part, to show the ridge changes that occurred due to variations in pressure used when depositing a print on a surface. The study had 21 volunteers provide 10 sequentially laid fingerprints from the same finger. These prints were converted to a digital format. Each group's 10 fingerprints were individually overlaid onto each other in an effort to obtain the best possible agreement. Once this was done, the overlay percentage was determined. After all overlays were performed, additional data were collected to determine how ridge widths changed when there was a change in observable minutiae, presumably due to a decrease in the pressure used to generate the print. The data obtained indicate that, even when all variables other than the physical characteristic of the finger and the psychomotor capabilities of the volunteer are controlled, people are not able to generate prints that will perfectly overlay. Additionally, the data show that pressure distortion causes ridge widths to vary when prints are deposited. Moreover, minutiae loss in the print can also occur as a result of this type of distortion.