Security issues on digital watermarking algorithms

This paper gives a general introduction to the digital watermarking procedures and their security aspects. The first issue is to clarify unifying and differentiating properties of steganography and watermarking. Then the most important aspects of digital watermarking are reviewed by studying application, requirement and design problems. We put emphasis on the importance of digital watermark as an effective technology to protect intellectual property rights and legitimate use of digital images. In the paper we provide an overview of the most popular digital watermarking methods for still images available today. The watermarking algorithms are divided into two major categories of spatial and transform domains. Because of outstanding robustness and imperceptibility the transform domain algorithms are the mainstream of research. Popular transforms of images include the DFT (Discrete Fourier Transform) ([1, 2, 3, 4, 5]), DCT (Discrete Cosine Transform) ([1, 3, 6, 5]) and DWT (Discrete Wavelet Transform) ([1, 3, 4, 7, 6, 5]). In the paper we emphasize the advantageous features of DWT such as local time-frequency and multi-scale analysis, preserving the quality of host image and ensuring high robustness of watermark. Finally, we present three algorithms which are based on the combination of DWT and some other transformations like DFT ([4]), DCT ([6]) and the Arnold transform ([7, 6]). Finally, we discuss security requirements and possible attacks on the watermarking systems