Construction and detection of digital holographic watermarks

This study presents an optical watermarking scheme using a digital holographic technique. The digital holographic watermark is constructed by a modified Mach-Zehnder interferometric architecture and a constant-level embedding algorithm, and the watermark detection is optically implemented using VanderLugt 4-f correlator with a weighting matched filter. The detection procedure is a compromise between perceptual quality and correlation robustness, in which the weighting factor selection rule and optimal threshold for the watermarking scheme are given and analyzed. Additionally, the detected correlation is spatially separable and avoided interference from the cover image. Both analytical and experimental results are presented and discussed.