Study of Watermarking for Image and Text Based Applications

Abstract

Due to the rapid development of multimedia and communications technologies, issues related to data vulnerability and copyrights violation has increased. Digital content can be manipulated and reproduced effortlessly. Consequently, there is a considerable requirement for techniques aimed at content protection and authentication. Watermarking techniques can provide copyrights enforcement and authentication to prevent the illegitimate use of digital content. These techniques can be classified into two categories i.e. robust watermarking and reversible watermarking. In this thesis, research work is carried out in three phases. The first phase proposes a robust watermarking technique, which is resilient against the geometrical attacks. It is helpful in executing copyright protection. In robust watermarking, watermark is able to survive in case of attack on the digital content and can be successfully retrieved on extraction. The proposed technique exploits both the robust image feature points and local Zernike moments for embedding secret information. Delaunay tessellation is employed to divide an image into distinct triangular segments based on robust features identified using Harris detector. Zernike moments are calculated for each selected triangular segment, and then the watermark is embedded in the magnitude of Zernike moments using dither modulation. In the second phase, a reversible watermarking technique is proposed. Reversible watermarking is a special type of watermarking technique in which watermark is extracted along with restoration of the host media. Whereas, in case of robust watermarking, we are not able to retrieve the original image. Such watermarking system finds its application in medical and law enforcement, etc. The proposed watermarking scheme is based on pixel value ordering. Image is divided into sub blocks and each block is assessed using a threshold value. If the block belongs to the smooth category, watermark bit is embedded. In contrast, if it is classified as rough block, then the sub block is left unchanged. This technique does not require a location map since it uses histogram shifting. In third phase, the watermarking approaches and their applications for the protection DNA sequences are explored. In DNA watermarking, which is type of text xii watermarking; watermark information should be embedded in DNA sequence in such a way that it should not raise any functional disorders in the living organism. A watermark is embedded in a DNA sequence through synonymous substitution of nucleotides. The proposed approach ensures Amino Acid conservation, efficient utilization of the available embedding space in DNA sequences, and achieves mutation resistance by since it employs Reed-Solomon codes. The performance of these techniques has been evaluated on the standard test datasets. In some of the cases, the proposed watermarking approaches performed better than the recent existing approaches and showed comparable performance in other cases. The first technique finds its application in protecting the copyrights of the owner. The second watermarking technique can be used in applications where significant amount of data needs to be embedded e.g. information related to the patient in medical images. The third technique related to the DNA watermarking can be used for protection of DNA sequences and also to provide biological data storage as large amount of data can be stored.