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.