A Cost Effective Scheme for Content Verification and Access Control of Quality of an Image

This paper proposes a data hiding method that integrates access control and authentication of digital image in a single platform. First of all a content dependent binary watermark is generated based on discrete cosine transform (DCT) coefficients of a set of blocks (8 times 8), that are selected pseudo randomly on the basis of the key supplied. The binary watermark is then embedded into the DCT coefficients of another set of selected blocks (8 times 8) using Spread Spectrum (SS) modulation. The block-based watermarking is semi-fragile in nature, which in turn leads to the ease of tamper detection for the content of the host data. The percentage matching between the extracted and the generated watermark at the watermark-decoding end indicates the amount of tempering made on the host data (authentication of content). On the other hand, the insertion of external watermark into a host image causes relative degradation in visual quality of the host image (cover) depending on the amount of watermark inserted. If this insertion process is reverted completely, the full quality of images can be accessed. This way the proposed watermarking scheme may find its use as access control of the cover image. The stimulation results have shown the validity of both the claims.