Local quaternion polar harmonic Fourier moments-based multiple zero-watermarking scheme for color medical images.

Zero-watermarking schemes are currently dedicated to resisting general desynchronization attacks, such as rotation and scaling, but cannot effectively resist complex desynchronization attacks, such as translation, cropping, length–width ratio changing, UnZign, and zero-padding. To this end, a robust zero-watermarking scheme resistant to complex desynchronization attacks was proposed in this paper based on local feature regions (LFRs) and quaternion polar harmonic Fourier moments (QPHFMs). First, the stable feature points of original color medical images were extracted with a speeded-up robust feature (SURF) operator; then, the stable LFRs were obtained through a feature scale-adaptive process and scale-standardized tests. Finally, the QPHFMs of the LFRs were calculated, and multiple feature sequences were constructed using their magnitudes and binarized to generate multiple zero-watermarks. The experimental results indicate that the proposed scheme can not only resist common image processing attacks and general desynchronization attacks but also robustly resist complex desynchronization attacks, such as translation, cropping, length–width ratio changing, UnZign, and zero-padding. The proposed scheme is superior to the state-of-the-art LFR-based multiple embedded watermarking schemes and zero-watermarking schemes.