The influence of biological sex on latent fingermark aging as examined by the color contrast technique.

This research further expands previous studies in which color contrast between ridges and furrows was examined as a possible age indicator for latent fingermarks. Here, the variable biological sex and its influence on aging were investigated. A total of 756 sebaceous-rich impressions from seven males and seven females were deposited on glass and polystyrene plastic and aged in the dark for three months. At nine discrete times, random fingermarks were visualized with a titanium dioxide-based powder (TiO2 ), photographed, and edited in Photoshop® to collect pixel color data. Two color contrast-related metrics, mean color intensity (MI) and intensity amplitude (IA), were analyzed to determine whether the aging processes of biological male and female fingermarks were equivalent. These metrics revealed that impressions from the different biological sexes behaved in a similar manner over time. However, significant effects between substrates were observed. Quadratic regression models best represented the aging trends based on the MI and IA metrics for both male and female fingermarks. The correlation coefficients (R) and coefficients of determination (R2 ) were moderate to strong for impressions on glass but weaker for plastic. These findings indicated that biological male and female fingermarks could be incorporated into a single universal age estimation model per substrate when utilizing color contrast as an age indicator. Nonetheless, future studies are needed to better understand aging processes on plastic when using this methodology and to determine the life expectancy (i.e., the potential for identification) of latent fingermarks beyond three months.

Repeatability and reproducibility of the color contrast technique for fingermark age estimation applications.

This research complements previous studies in which color contrast between ridges and furrows of latent fingermarks was investigated as a potential aging parameter. In this case, the robustness of the technique has been tested by including five female and five male donors who deposited sebaceous-rich latent fingermarks onto ceramic tile and polystyrene plastic as well as flat and rolled inked fingerprints on commercially available ten-print cards. Fresh latent fingermarks were visualized with either carbon black or titanium dioxide powder (TiO2 ) and inked fingerprints were imprinted in succession without re-charging ink. The mean intensity (MI) and intensity amplitude (IA) metrics of the color histogram were collected from each image for statistical analyses. The goals were to detect any differences within and between the analysts' own interpretation of the protocol as well as examine how color contrast may be influenced by donor, substrate, biological sex, powder type, and the quantity of ink deposited. Results show that the color contrast metrics (MI and IA) are repeatable and reproducible and not affected significantly by donor, sex, deposition pressure, or distortion. However, the metrics were sufficiently sensitive to distinguish substrate and powder types and to detect different quantities of ink. The statistical analyses confirm and expand upon previous observations regarding the reliability of MI and IA as metrics that could eventually be used to estimate the age of a latent fingermark. At the same time, it was revealed that the technique needs further improvement and standardization by including a universal "white color standard" to conduct image comparisons.