Yusnita Yusof

Digital watermarking for digital images using wavelet transform

The field of digital watermarking has recently seen vast interests covering theoretical studies, novel techniques, attacks and analysis. This is due to the fact that over the last 15 years, the watermarking community has focused on developing and introducing new techniques for watermark embedding and detection. Analysis of these techniques leads to methods for attack and development of countermeasures which then used to discover faults and limitations in applications, encouraging the development of better ones. In this paper, comprehensive overview of digital watermarking are discussed. This includes the general model, types, applications and future trends of current implementations. The proposed technique is described and analyzed. The paper concludes with future plans of the chosen method in digital watermarking.

Imperceptibility and robustness analysis of DWT-based digital image watermarking

Digital watermarking is distinctive depending on the techniques used and its intended applications. This paper concentrates on invisible digital image watermarking using discrete wavelet transform. The work flow involves watermark embedding, attacks and watermark extraction. Two methods are proposed and analyzed to imply the imperceptibility and robustness, among the most important criteria of digital watermarking, using three types of attacks - JPEG compression, blurring and histogram equalization. The results are compared through subjective visual inspections and calculative measurements using PSNR for watermark imperceptibility and SSIM index for watermark robustness.

State-of-the-art digital watermarking attacks

Digital watermarking is a huge research area which is progressively growing. It covers theoretical studies, novel techniques, attacks and performance analysis. An embedded watermark may unintentionally or inadvertently be impaired by such processing. Other types of processing may be applied with the explicit goal of hindering watermark reception. In watermarking terminology, an “attack” is any processing that may impair detection of the watermark or communication of the information conveyed by the watermark. Broadly it can be classified as Intentional Attacks and Non-Intentional Attacks. The processed watermarked data is then called “attacked data”. An important aspect of any Watermarking scheme is its robustness against attacks. The notion of robustness is intuitively clear: A watermark is robust if it cannot be impaired without also rendering the attacked data useless. Watermark impairment can be measured by criteria such as miss probability, probability of bit error, or channel capacity. For multimedia, the usefulness of the attacked data can be gauged by considering its perceptual quality or distortion. Hence, robustness can be evaluated by simultaneously considering watermark impairment and the distortion of the attacked data. An attack succeeds in defeating a watermarking scheme if it impairs the watermark beyond acceptable limits while maintaining the perceptual quality of the attacked data. In this paper, JPEG compression (quality 50 and 75), noise (Gaussian noise), distortion (blurring) and contrast enhancement (histogram equalization and intensity adjustment) are testified. Results shown that embedding gain and DWT decomposition subbands were among the contribute against attacks performed.