Abstract— A new blind gray-level watermarking scheme is described. In the proposed method, the host image is first divided into 4×4 non-overlapping blocks. For each block, two first AC coefficients of its Hadamard transform are then estimated using DC coefficients of its neighbor blocks. A gray-level watermark is then added into estimated values. Since embedding watermark does not change the DC coefficients, watermark extracting could be done by estimating AC coefficients and comparing them with their actual values. Several experiments are made and results suggest the robustness of the proposed algorithm. Keywords—Digital Watermarking, Image watermarking, Information Hiden, Steganography. I. INTRODUCTION owadays, there are many multimedia transmissions on the network. Because of the easy access to digital contents, copy control of digital data became an important issue. In the recent years, there was a strong demand for secure copyright protection techniques for multimedia data. Copyright protection of digital images is defined as the process of proving the intellectual property rights. Digital watermarking is a technique, which secretly embeds digital data into the material to identify the origin, owner, informal user, etc. Digital watermarks must be resilience against attempts to remove the hidden data. There are three kinds of digital watermarking techniques according to their embedding purpose: robust, fragile, and, semi-fragile[1]. A robust watermark withstands malicious attacks, such as scaling, rotation, filtering, and compression. This kind of watermarking is usually used for copyright protection. Fragile watermarks can detect any unauthorized modification in an image, and therefore, they are quite suitable for an authentication purpose. However, a semi-fragile watermark is adopted to detect the unauthorized modifications, and, at the same time, it must survive some authorized image processing operations. Depending on the application, the original host image is or is not available to the watermark recovery system. While most watermarking techniques require the original picture, there is a great interest in techniques that do not require the original S. Saryazdi is with the Electrical Engineering Department of Shahid Bahonar University of Kerman, Kerman, Iran ( phone: (98) 341-3335711, fax: (98) 341-3335711, e-mail: saryazdi@mail.uk.ac.ir). H. Nezam Abadi pour is with the Electrical Engineering Department, Shahid Bahonar University of Kerman, Kerman, Iran (e-mail: nezam@mail.uk.ac.ir). data for recovering, i. e. blind watermarking techniques. That is because of the larger applications of such techniques [1]. Watermark embedding could be done in spatial or transform domain. Transform domain techniques are more robust and resistant to various attacks, and, most watermarking techniques use frequency domain to embed data. In [2], Cox et al. Describe a method for embedding a binary watermark sequence in the highest magnitude DCT coefficients. Hsu and Wu [3,4] use the middle frequency coefficients of DCT/Wavelet transform to embed a binary watermark. These mentioned methods are robust against image processing. Their main drawback is requiring the original image to extract the watermark. Wang et al. [5] describe a kind of blind watermarking based on relative modulation of the DCT coefficient value by referring to its estimated one. In their method, the DC values of a 3×3 neighborhood of 8×8 blocks are used to estimate the AC coefficients of central block. In each group of nine 8×8 blocks, five bits of watermark are embedded by modulating the first five DCT AC coefficients, in central block, with the following rule: Set i i ' AC AC to embed bit “1” Set i i ' AC AC to embed bit “0” Where, i AC and i ' AC are the real and estimated value of the AC coefficients, respectively. The watermark recovery is done by comparing i AC and its estimated value. If i i ' AC AC , then the extracted bit is “1”, otherwise, it is “0”. Several watermarking techniques in Hadamard domain have been proposed[6, 7, 8]. Gilani and Skodras[8], describe a watermarking scheme based on multi-resolution Hadamard transform. Their scheme is robust against most image processing and geometric operations. In[9], Fei et al. attempt to find a suitable transform domain to watermark images robust against JPEG compression attack. They show that the choice of the transform domain depends on the type of the embedded information. If the watermark is embedded by repetition coding, then the Hadamard transform gives the best results. In this paper we propose a blind scheme for gray-level data embedding in Hadamard Domain. In the next section we review the Hadamard Transform. The proposed method will be described in section III. In section IV the experimental results are presented, and, finally, in section V a conclusion is given. A Blind Digital Watermark in Hadamard Domain Saeid Saryazdi, Hossein Nezamabadi-pour N World Academy of Science, Engineering and Technology 3 2005 126