Optical robust zero-watermarking scheme based on chaotic facial phase masks and diffractive imaging

Currently, most optical watermarking schemes adopt an embedding strategy, which often leads to a trade-off between watermark imperceptibility and robustness. Additionally, the encryption keys used are typically not linked to user identity, posing significant security risks in the event of key leakage. To address these issues, this paper proposes an optical robust zero-watermarking scheme based on chaotic facial phase masks and diffractive imaging. In the proposed optically robust zero-watermarking scheme, the original watermark is first encoded into a noise-like diffraction intensity image using a chaotic facial phase mask and diffraction imaging. This encoded watermark is then XORed with the texture features extracted from the host image via variational image decomposition, thereby generating the zero-watermark. During the decoding process, the original watermark can be approximately losslessly recovered from the zero-watermark using the texture features of the host image, an iterative phase retrieval algorithm, and the authenticated user's facial image. Since the encryption and decryption keys are tied to the user's facial features, which do not require storage or transmission, the proposed scheme offers a high level of security. Moreover, extensive experimental results and analyses demonstrate that the proposed optical zero-watermarking method exhibits strong robustness against both image processing operations and geometric attacks.