Digital Image Watermarking In DCT Domain

Digital Image watermarking is the process that embeds data called watermark in to multimedia object such that the watermark can be extracted or detected to make an assertion about the object. Watermarking is either “visible” or “invisible”. The growth of high speed computer networks and internets, in particular, explore the means of new business, scientific, entertainment and social opportunities. Ironically the cause for the growth is also of the apprehension use of digital formatted data. The ease with which the digital information can be duplicated and distributed has led to need for effective copyright tools. Various software products have been recently introduced in attempt to address these concerns. It is done by hiding data within digital audio, image and video files. Digital image watermarking is one of the way of data hiding techniques. Watermarking can be done in spatial and transform domain. The basic problem in watermarking in spatial domain is that the watermark is more fragile i.e., more susceptible to attacks than transform domain. The reason for choosing the transform domain (DCT and DFT is that the characteristics of human vision system(HVS) are better captured by spectral coefficients. For eg. Low frequency coefficients are perceptually significant, which means alterations to those components might cause significant distortion to original image On the other hand, high frequency coefficients are considered insignificant: thus ,processing techniques such as compression tend to remove high frequency coefficients aggressively. Keywords-Copyright protection, digital image watermarking, spatial domain, transform domain, Discrete Cosine Transform(DCT), Discrete Fourier Transform(DFT , Peak Signal to Noise ratio(PSNR), Correlation.