Reversible watermarking with digital signature chaining for privacy protection of optical contactless captured biometric fingerprints - a capacity study for forensic approaches

The FRT-MicroProf 200 CWL (Chromatic White Light) sensor, typically used for the measurement of surface properties for quality assurance purposes, is adapted and used for the contactless, non-invasive lifting of latent fingerprint traces. To the resulting high-resolution biometric data, invertible fragile image watermarking is applied, to assure authenticity and integrity of the data in a forensic investigation. Privacy protection is added by encryption and substitution of the fingerprint area. The scheme is extended to be used in a digital signature chain scenario with hierarchical access for further forensic investigation and the generation and preservation of a chain of custody. The capacity of the introduced watermarking protocol is evaluated in theory and in practical tests using 90 image samples (16bit grayscale, 30 intensity fingerprint images: Ø6.5bpp, 30 3d-topography fingerprint images: Ø11.2bpp and 30 standard images: Ø1.2bpp, different sizes and embedding areas) showing very high capacities especially for fingerprint images.