One of challenges encountered in information bit hiding is the reliability of information bit detection. This paper addresses the issue and presents an algorithm in the discrete cosing transform (DCT) domain with a communication theory approach. It embeds information bits (first) in the DC and (then in the) low-frequency AC coefficients. To extract the hidden information bits from a possibly corrupted marked image with a low error probability, we model information hiding as a digital communication problem and apply Bose-Chaudhuri-Hocquenghen channel coding with soft-decision decoding based on matched filtering. The robustness of the hidden bits has been tested with StirMark. The experimental results demonstrate that the embedded information bits are perceptually transparent and can successfully resist common signal processing procedures, jitter attack, aspect ratio variation, scaling change, small angle rotation, small amount cropping, and JPEG compression with quality factor as low as 10. Compared with some information hiding algorithms reported in the literature, it appears that the hidden information bits with the proposed approach are relatively more robust. While the approach is presented for gray level images, it can also be applied to color images and video sequences.

An image watermarking scheme in a DCT domain is proposed, it is adaptive in that a different strength of watermark is applied to different blocks according to their block classification. For the classification, visual masking (both luminance and texture masking) is taken into account. Consequently, the watermarks thus generated are robust and invisible.

Digital watermarking has been researched extensively due to its potential use for data security and copyright protection. Much of the literature has focused on developing invisible watermarking algorithms. However, not much has been done on visible watermarking. A visible watermark is apparently needed for copyright notification. This work proposes a new framework of visible watermarking based on image fusion, a common technique used in combining images acquired from different modalities. To better protect the host features and increase the robustness of the watermark, the dual-tree complex wavelet transform (DT-CWT) is used. A new classification strategy is proposed to classify complex wavelet coefficients into 6 classes with different perceptual significance. The embedding decision can be made based on the classification information. Small watermark coefficients are prohibited from embedding. In the host edges, the insertion of watermark energy is controlled by using the inversely proportional embedding scheme to better preserve the sensitive region, while in other regions, the embedding strength becomes stronger as texture activity increases. This work also addresses the problem of low-pass subband watermark embedding, which is a special issue of visible watermarking. Experimental results show that the proposed algorithm yields significantly superior image quality than the current DCT-based method.

An adaptive filtering algorithm for artefact removal in block coded images is presented. Based on an analysis of block artefacts in the frequency domain, the edge image is notch filtered and then used for a neighbourhood analysis. A space-variant filter is applied to the coded image adaptively, dependent on a frequency analysis.

Both watermark structure and embedding strategy affect robustness of image watermarks. Where should watermarks be embedded in discrete cosing transform (DCT) domain in order for the invisible image watermarks to be robust? Though many papers in the literature agree that watermarks should be embedded in perceptually significant components, dc components are explicitly excluded from watermark embedding. In this letter, a new embedding strategy for watermarking is proposed based on a quantitative analysis on the magnitudes of DCT components of host images. We argue that more robustness can be achieved if watermarks are embedded in dc components since dc components have much larger perceptual capacity than any ac components. Based on this idea, an adaptive watermarking algorithm is presented.We incorporate the feature of texture masking and luminance masking of the human visual system into watermarking. Experimental results demonstrate that the invisible watermarks embedded with the proposed watermark algorithm are very robust.