Research On Digital Image Watermarking Technology Against Geometric Attacks

Information hiding is the technique to embed secret information for covert transmission, which is the very active and important component in the research of information security field. Digital watermarking is an important branch of information hiding, which is a kind of technique to solve multimedia information security problem on network, and is the crossed subject involving information security, multimedia signal processing, pattern recognition and etc. At present, watermarking technique becomes an effective means to multimedia copyright authentication and its integrity safeguarding. But, its performance of withstanding geometric attacks seriously restrictes the use range of digital watermarking. Resistance to geometric attacks is the core and difficulty problem of digital watermarking, and it is also the bottleneck in practical use.This dissertation takes still images as examples, analyses the existing digital watermarking applications against geometric attacks, and studies the digital watermarking theory and techniques being fit for resisting the geometric attacks.Then, some algorithms are proposed to withstand the geometric attacks from three points of research: geometric invariant field, geometric correction, and pattern watermarking. The main contributions are enumerated as follows:First, the image watermarking scheme based on SIFT feature is proposed. We use the feature points to construct the Delaunay triangular mask, then, can make the triangles to against geometric attacks based on the SIFT points's ability of resisting geometric attacks. And, watermarking is embedded in the image content according the several-for-one principle by additive method.Second, a novel digital watermarking algorithm based on singular value decomposition is proposed .The algorithm makes singular value decomposition on blocks of amplitudes in frequency domain, and embed watermarks via modifying the sub-maximum singular value. Use the geometric invariant of singular value to realize the geometric invariant of watermarking application.Third, based on the point of geometric correction, two new watermarking means are proposed on the basis of the theories of invariant centroid and geometric moment. The geometric transformation could be corrected by the changes of three invariant centroids' coordinates or by exploiting the geometric moments of original image and watermarked image before the watermarking detection. Therefore, the corrupted watermarked image can be corrected and the watermarking can be correctly detected. The watermarking algorithms improved the ability which resists to geometric attacks.Finally, a geometrically robust watermarking method, which is not sensitive to synchronization, is proposed based on the centers which are detected by Harris corner detector. The structure of watermark pattern is elaborately designed, and then finds some maximum points according to the pattern. Watermarking information is embedded in these points. And the information can be extracted by analyzes these points. This method's complexity is reduced because no additional work is needed to meet the synchronization requirement and no area partitioning and normalization are needed.At last, the deficiencies in the dissertation are summarized, and some open issues in digital watermarking as well as the future work are presented.