RST invariant digital image watermarking

Abstract

Digital image watermarking has been proposed as a method to ensure the copyright protection and credibility of images by means of embedding a known piece of digital data into host images. To be useful, a good watermarking scheme should be robust against all known attacks to a certain degree based on requirements. In this thesis, we propose a novel digital image watermarking scheme that is invariant to rotation, scaling, and translation (RST). We embed watermark in the log-polar mapping (LPM) of the Fourier magnitude spectrum of original image, and use the phase correlation between the LPM of the original image and the LPM of the watermarked image to calculate the displacement of the watermark positions in LPM domain. The exhaustive search method is used to retrieve the watermark if the original image is unavailable. Spread spectrum technique and perceptual model are used to enhance the security and to achieve the optimum balance between invisibility and robustness. Stochastic analysis is used to determine the optimum threshold to minimize the total false probability of detection. In this thesis, we discuss all these in detail and show how they work with the main watermarking scheme to give better results. We implement this watermarking algorithm to analyze its performance. The evaluations demonstrate that the scheme is invariant to rotation and translation, invariant to scaling when the scale is in a reasonable range, and very robust to JPEG compression and other attacks.