Efficient copyright protection for three CT images based on quaternion polar harmonic Fourier moments

The current zero-watermarking scheme mainly offers the copyright protection to one image. Although the scheme can be used for many images repeatedly, the repeat operation requires a lot of time and large storage space. Using the quaternion polar harmonic Fourier moments (QPHFM), the paper considers three CT images as a whole to construct the key image and proposes a robust zero-watermarking algorithm offering the copyright protection to three CT images simultaneously, improving the efficiency of watermarking system and saving the storage space. The algorithm first considers the three CT images as three imaginary parts of an array of pure quaternion and calculates their QPHFM and then constructs feature image using the amplitude of QPHFM, and finally makes the chaotic scrambling to the feature image and then the XOR operation to the feature image and watermark image to generate key image. Experiment results prove the proposed scheme can resist common image processing attacks and geometric attacks effectively and thus can be well applied to the copyright protection of three images. (C) 2019 Elsevier B.V. All rights reserved.