DWT BASED DUAL WATERMARKING SCHEME FOR RIGHTFUL OWNERSHIP AND SECURE IMAGE AUTHENTICATION

Abstract

The availability of versatile multimedia processing software and the far-reaching coverage of the interconnected networks have facilitated flawless copying, manipulations and distribution of the digital multimedia (digital video, audio, text, and images). The ever advancing storage and retrieval technologies have also smoothed the way for large-scale multimedia database applications. However, abuses of these facilities and technologies pose pressing threats to multimedia security management in general, and multimedia copyright protection and content integrity verification in particular. Although cryptography has a long history of application to information and multimedia security, the undesirable characteristic of providing no protection to the media once decrypted has limited the feasibility of its widespread use. For example, an adversary can obtain the decryption key by purchasing a legal copy of the media but then redistribute the decrypted copies of the original .In response to these challenges; digital watermarking techniques have been proposed in the last decade. Digital watermarking is the procedure whereby secret information (the watermark) is embedded into the host multimedia content, such that it is: (1) hidden, i.e., not perceptually visible; and (2) recoverable, even after the content is degraded by different attacks such JPEG compression, noise, horizontal and vertical flips etc. The two basic requirements for an effective watermarking scheme, imperceptibility and robustness, conflict with each other. The main focus of this thesis is to provide good tradeoff between perceptual quality of the watermarked image and its robustness against different attacks. For this purpose, we have discussed a robust digital watermarking technique in discrete wavelet (DWT) domain. This scheme employs a contrast sensitivity based human visual system (HVS) model. The iv

HVS models give us a direct way to determine the maximum strength of watermark signal that each portion of an image can tolerate without affecting the visual quality of the image. The proposed work develops a novel approach of embedding both visible and invisible watermarks into cover image. Visible watermark is used only to distract the hacker /unauthorized user as actual watermark is inserted invisibly. This increases the security two fold as visible watermark act as copyright logo and invisible serves the purpose of authentication. This is carried out by embedding primary watermark visibly using alpha blending and the DWT coefficients of the host image have been modified for embedding invisible secondary watermark. The proposed approach incorporates both blind and non blind methods into one watermarking scheme and work well on grayscale as well as color images. Performed objective and subjective analysis proves the efficiency of proposed approach.