How contact pressure, contact time, smearing and oil/skin lotion influence the aging of latent fingerprint traces: First results for the binary pixel feature using a CWL sensor

Determining the age of latent fingerprint traces found at crime scenes is an unresolved research issue since decades. In prior work, we have suggested to use optical, non-invasive image sensory in combination with a new aging feature called `binary pixel´ (shown to have a characteristic logarithmic aging tendency on hard disk platters) to solve this important research challenge. In this paper, we evaluate the influence of the fingerprint application process (such as contact pressure, contact time, smearing of the fingerprint or contamination with skin lotion or oil) on the aging curves of the binary pixel feature (inter-application-factor-variance). We furthermore evaluate differences of fingerprint traces applied in a similar way (intra-application-factor-variance). Examining 25 fingerprint samples of a test subject with a total of 500 scans, we show that the application of substances to a finger seems to increase the present amount of residue and that substances containing water increase the aging speed of a fingerprint trace significantly.