Laser-Induced Visualization of Latent Fingerprints on Metal Surfaces

Latent fingerprints (LFPs) are pivotal evidence in criminal investigations, yet their direct observation poses inherent challenges, necessitating advanced visualization techniques. Here, an innovative one-step laser-based methodology is presented for the rapid and accurate visualization of LFPs on metal surfaces. Gray value analysis is utilized to compare the optical contrast between the ridges and valleys of original and visualized fingerprints. Additionally, an orientation field method is employed to evaluate the texture quality of visualized fingerprints. The results demonstrate that laser irradiation significantly enhances the recognizability and pattern fidelity of LFPs by inducing differential oxide deposition: ridges, enriched in skin secretions, exhibit reduced oxide accumulation compared to valleys, thereby amplifying ridge-valley optical contrast. Furthermore, the visualized fingerprints exhibit excellent resistance to abrasion. Importantly, this method demonstrates broad applicability across surfaces with varying roughness levels and diverse metal types. This study establishes a robust and versatile tool for the rapid and accurate visualization of LFPs, offering transformative potential for forensic investigations.