Analysis of Digital Watermarking Techniques

Abstract

The enormous popularity of the World Wide Web in the early 1990's demonstrated the commercial potential of offering multimedia resources through the digital networks. Since the commercial interests seek to use the digital networks to offer digital media for profit, they have a strong interest in protecting their ownership rights. Digital watermarking has been proposed as one way to accomplish this. There are different watermarking techniques used now days and some of them are discussed in the present work. The main aim of watermarking is to protect and authenticate the original data under various attacks. Therefore, the watermarking should be robust against attacks. In the present work watermarking in spatial domain, transformation domain and fractional domain are analyzed under two attacks i.e. addition of AWGN and compression. In spatial domain three techniques i.e. least significant bit substitution, correlation based and CDMA spread spectrum are discussed. In frequency domain, DCT-based watermarking is implemented. In fractional domain, Fractional Discrete Cosine is used for watermarking. For all the techniques the various parameters such as: peak signal to noise ratio (PSNR), root mean square error (RMSE) and bit error rate (BER) are calculated and based on that the watermarking techniques are compared. In fractional domain, two-dimensional Fractional Discrete Cosine Transform (FRDCT) is used for watermarking. Watermarking in the fractional domain benefits from its extra degree of freedom that is provided by its fractional order (a). The parameter 'a' can be interpreted as a rotation by an angle in time-frequency domain. By adjusting 'a' to different values, FRDCT can achieve higher PSNR and lower RMSE without visual degradation of watermarked image.