1 Ubiquitous Computing and Communication Journal Volume 2 Number 5 www.ubicc.org Page AN EFFICIENT BLOCK-BY-BLOCK SVD-BASED IMAGE WATERMARKING SCHEME R. A. Ghazy # , N. A. El-Fishawy # , M. M. Hadhoud $ , M. I. Dessouky # and F. E. Abd El-Samie # # Dept. of Electronics and Elect. Communications., Fac. of Electronic Eng., Menoufia Univ., 32952, Menouf , EGYPT. $ Dept. of Inform. Tech., Faculty of Computers and Information , Menoufia Univ., 32511, Shebin Elkom , EGYPT. E-mails: eng_rasg@yahoo.com, nelfishawy@hotmail.com, mmhadhoud@yahoo.com and fathi_sayed@yahoo.com ABSTRACT This paper presents a block based digital image watermarking scheme that is dependent on the mathematical technique of singular value decomposition (SVD). Traditional SVD watermarking already exists for watermark embedding on the image as a whole. In the proposed approach, the original image is divided into blocks, and then the watermark is embedded in the singular values (SVs) of each block separately. This segmentation and watermarking process makes the watermark much more robust to the attacks such as noise, compression, cropping. Watermark detection is implemented by extracting the watermark from the SVs of the watermarked blocks. Experiments show that extracting the watermark from one block at least is enough to ensure the existence of the watermark. Keywords: Image Processing, Watermarking, Singular Value Decomposition. 1 INTRODUCTION The spreading of digital multimedia nowadays has made copyright protection a necessity. Authentication and information hiding have also become important issues. To achieve these issues, watermarking technology is used. Several researchers have worked in the field of watermarking for its importance [1-11]. The work in this field has led to several watermarking techniques such as correlation-based techniques, frequency domain techniques, DFT based techniques and DWT based techniques [2]. Watermarking means embedding a piece of information into multimedia content, such as video, audio or images in such a way that it is imperceptible to a human observer, but easily detected by a computer or detector [1]. Before the emergence of digital image watermarking, it was difficult to achieve copyright protection, authentication and data hiding but now it is easy to achieve these goals using watermarking techniques. Every watermarking algorithm consists of an embedding algorithm and a detection algorithm. Watermarking has several properties such as robustness, fidelity, and tamper-resistance [1]. The robustness means that the watermark must be robust to transformations that include common signal distortions such as digital-to-analog, analog-to-digital conversion, and lossy compression. Fidelity means that the watermark should be neither noticeable to the viewer nor degrading for the quality of the content. Tamper- resistance means that the watermark is often required to be resistant to signal processing algorithms. The existence of these properties depends on the application. The watermark can be embedded in the spatial domain or in the transform domain [2]. The SVD mathematical technique provides an elegant way for extracting algebraic features from an image. The main properties of the SVD matrix of an image can be exploited in image watermarking. The SVD matrix of an image has good stability. When a small perturbation is added to an image, large variation of its SVs does not occur [3], [4]. Using this property of the SVD matrix of an image, the watermark can be embedded to this matrix without large variation in the obtained image. Liu et al. have proposed an SVD based watermarking scheme in which the watermark is added to the SVs of the whole image or a apart of it [3]. A single watermark is used in this scheme which may be lost due to attacks. To avoid this disadvantage, we propose an approach in which , the original image is segmented into blocks and the watermark is added to the SVs of each block in a modified manner. The SVs of the modified