Image Hashing Based On Fractional Fourier Transform

As one of information security technology, image hashing can turn different size pictures into a robust hash sequence. It is used in the fields of image retrieval, image authentication and copyright protection, etc. The research on image hash algorithm attracts the interest of scholars all over the world. At the same time, a new tool for time-frequency analyzing, called fractional Fourier transform, is developing rapidly in recent years. Due to its excellent performance in time-frequency analysis, it has been applied widely in signal processing field.After studying current hash algorithms in depth, taking static gray image as fundamental research object, thorough research has been conducted to the hash algorithms in fractional Fourier transform domain. An image hash algorithm based on fractional Fourier transformation is proposed in this thesis.Making use of the characteristic of fractional Fourier Transform, the transform order is used as one of the secret keys for Hash generation and the pseudo-random data set as another. Thus, the proposed Hash algorithm realizes the double secret keys for Hash sequence generation and enhances the security of it. On the other hand, owing to the characteristic of Image Fractional Fourier Transform for feature detection, this algorithm is free-collision and robust enough to different attacks, such as filtering, rotation and JPEG compression and so on. Experimental results show that the proposed Hash algorithm has well performance in the robustness, free-collision and security.