Robust Watermarking of Greyscale Images in Frequency Domain by Optimizing Watermarking Sterngth Parameter

Unlimited number of replicas of the original content can be made from unprotected digital content. Billions of bits of data is created in every fraction of a second. Also, with the advent of internet, creation and delivery of digital data (images, video and audio files, digital repositories and libraries, web publishing) has grown many fold. Since copying a digital data is very easy and fast too so, issues like, protection of rights of the content and proving ownership, arises. Digital watermarking came as a technique and a tool to overcome shortcomings of current copyright laws for digital data. The specialty of watermark is that it remains intact to the cover work even if it is copied. So to prove ownership or copyrights of data watermark is extracted and tested. It is very difficult for counterfeiters to remove or alter watermark. As such the real owner can always have his data safe and secure. The focus of this dissertation is the watermarking of grayscale images. Different watermarking techniques exists, in spacial (pixel) and frequency (signal) domain, which are resistant to all types of attack, scalar or geometric. In this work, a method for watermarking of grayscale images in frequency domain is proposal. The standard method of Fast Fourier Transform based image watermarking is augmented with cost function based on watermark strength and similarity factor. Mathematical techniques are presented which embeds watermark in frequency domain, while at the same time, maintaining the robustness or watermark under various attacks. The simulation is done using MATLAB and results are compared with existing techniques of DFT based watermarking. Comparison of the results are presented which shows a considerable improvement in Peak Signal to Noise Ratio.