The use of digital watermarks with digital signatures and their applications on multimedia data

In this thesis, two fragile watermarking techniques having both high accuracy localization resolution property and security against attacks are proposed for image authentication. The first proposed technique is based on Hierarchical Watermarking Technique. In the proposed technique, named ?Hierarchical Tree Structure Watermarking Technique?, it has been suggested to divide the image into the sub-blocks using ceiling and floor functions. Furthermore, two different signature algorithms are employed in the hierarchical tree structure. It has been shown by the experimental work that the proposed technique has better performance than the Hierarchical Watermarking Technique. The second proposed fragile watermarking technique is based on dependent block structure. In this approach, called ?A Sub-Block Based Fragile Watermarking Technique?, both a novel dependent block structure and a watermark verification algorithm are developed. This verification algorithm provides more accurately resolution at the determination of tamper region up to 4 times. In addition, it has been suggested to use two separate signature algorithms employing the proposed technique. In case of employing more secure and longer signature algorithms, this suggestion provides a superior tradeoff between security and localization resolution. The experimental results demonstrate that the proposed sub-block based fragile watermarking technique shows better performance than the HBC2 Watermarking Technique mentioned in the literature. Keywords: Fragile Watermarking, Image Authentication, Information Hiding, Security