SECURE WATERMARKING OF DIGITAL DATA FOR COPYRIGHT PROTECTION

Abstract

The exponential growth of technologies, media to access the same and simplification of the related processes has spurred an unprecedented growth in this domain. When the digital media is generated, transmitted and distributed over multiple devices and interconnecting networks, maintenance of its authenticity and ensuring the intellectual rights of the owners and authorized users is of utmost significance. With the progressive evolution in technology and distribution networks, prevention of widespread dissemination of sensitive and private information is an arduous challenge. The attacks on the secured information are designed so as to enable unscrupulous users to gain illegitimate access to the secured data, who may tamper with its contents and/or undermine the associated intellectual property rights of the owner and authorized users. To effectively deal with problems of such kind, we need to ensure that the content of the data being transmitted is minimally modified, if not left unchanged, on exposure to such attacks. Further, the identity of the owner and her intellectual rights should be protected from infringement. The above requirements are pivotal for maintaining the authenticity of the data, protection of the content from undesirable alterations during transmission and assertion of the copyright of its rightful owners and users. As a solution to counter this menace, digital watermarking of the cover work has been proposed in this field. It serves the different purpose highlighted above by embedding secret data (watermark) in the cover work, through minimal modification of its content. The immediate advantage of this approach is the level of imperceptibility of the v embedded watermark can be suitably modulated. Further, depending upon the kind of anticipated attacks in the channels of distribution and transmission, the scheme can be configured to provide the required level of robustness and security. Embedding the data in this manner also leads to better security too as the location and content of the watermark within the cover work are difficult to ascertain. Some schemes have also been designed to offer good capacity in terms of the quantum of watermarking data which can be embedded, thus boosting the robustness and security of the methodology. While watermarking of a multitude of media including text, video, printed circuits etc. have been undertaken, all of them are based on the fundamental challenges seen in the watermarking of 1-D and 2-D data. To this extent, the initial works in the domain revolved around addressing the different shortcomings in the techniques related to the watermarking of audio and images. This was crucial as addressing these problems provided more clarity on similar problems faced in watermarking of cover work with higher data volume and complexity. First, we discuss about watermarking of 1-D data. Watermarking of audio signals is considered as a pertinent challenge owing to the feature of non-degradation of audio quality post insertion of the watermark, for ensuring non-distinguishability from the original cover work, while maintaining the watermark imperceptibility. Further, the watermark should also continue to serve its purpose of copyright protection of the intellectual property and maintain robustness a variety of signal processing and distortive attacks. In fulfilment of the above key requirements and other vital characteristics of a good watermarking scheme viz. security and payload capacity, this dissertation outlines an effective methodology for watermarking of the audio signal in the time-frequency vi domain through the use of linear canonical transform (LCT). The embedded watermark was found to be survive wide range of attacks ranging from signal processing to audio quality distortive. Further, the technique provides good security and offers an appreciable payload capacity up to 15% of the audio signal length. Next, we shift our focus to 2-D and 3-D data. Here, we consider both grayscale and colour RGB images. For images specified in grayscale, strong watermarking decreases the invisibility. Contrary to this, weaker watermarking improves imperceptibility but reduces the robustness. For embedding the watermark, we deploy the image partitioning approach based on the psycho-visual redundancy. Watermark scrambling using Arnold Transform and subsequent embedding in the lowest frequency DWT sub-band of the image leads to improved security, robustness as well as the imperceptibility as compared to contemporary schemes. For 3-D colour (RGB) images, we adopt 2 approaches. As many image moments suffer from limited reconstruction ability, errors during numerical approximation, low stability and diminished feature integrity, this work provides a novel two-tiered zero watermarking framework for color images using Fractional Order Generic Polar Complex Exponential Transform (FrGPCET). Initially, the watermark is scrambled using quasi-affine transform. The stable fractional order moments are calculated in a fast and accurate manner, using higher order interpolators and Gaussian numerical integration. Through incrementally iterative pseudo-random selection and Otsu thresholding, an augmented moment feature vector is formed which is in-turn used for embedding the watermark. The second tier is focused towards increasing the imperceptibility by removing any background artifacts, and reducing information redundancy. It involves the vii sequential use of Discrete Cosine Transform and Huffman coding. Comparison with the state-of-the-art methodologies has shown that the proposed technique surpasses them in terms of watermark’s imperceptibility and robustness to different attacks. It is also inherently secure, offers good payload capacity, and can be implemented efficiently with nominal computational resources. Our second approach relies on increasing the similarity between the power spectra of the host and watermark images. We wish to minimize the severity of the attacks based on estimation of the MMSE. This leads to an energy efficient watermarking scheme offering contemporary imperceptibility and robustness against state-of-the-art watermarking techniques. The principles leveraged include inter alia graph signal processing, spectral graph wavelet, variational mode decomposition and local dominant orientation feature extraction. Each of them serves to enhance the strength of the watermarking in terms of imperceptibility, robustness, security, payload capacity and energy efficiency.