Robustness is one of the crucial important issues in watermarking. Robustness against geometric distortion and JPEG compression at the same time with blind extraction remains especially challenging. In this paper, a blind discrete wavelet transform-discrete Fourier transform (DWT-DFT) composite image watermarking algorithm that is robust against both affine transformation and JPEG compression is proposed. This algorithm improves the robustness via using new embedding strategy, watermark structure, 2-D interleaving, and synchronization technique. A spread-spectrum-based informative watermark with a training sequence are embedded in the coefficients of the LL subband in the DWT domain while a template is embedded in the middle frequency components in the DFT domain. In watermark extraction, we first detect the template in a possibly corrupted watermarked image to obtain the parameters of affine transform and convert the image back to its original shape. Then we perform translation registration by using the training sequence embedded in the DWT domain and finally extract the informative watermark. Experimental works have demonstrated that the watermark generated by the proposed algorithm is more robust than other watermarking algorithms reported in the literature. Specifically it is robust against almost all affine transform related testing functions in StirMark 3.1 and JPEG compression with quality factor as low as 10 simultaneously. While the approach is presented for gray-level images, it can also be applied to color images and video sequences.

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.

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.

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.

This paper presents a watermarking scheme with enhanced robustness owing to adaptive receiving and turbo code in addition to other measures. We embed a training sequence with informative watermark in the original image. A new adaptive receiver is developed, which is adjusted adaptively according to the responsive distribution of the training sequence. Together with carefully designed data embedding techniques, concatenated coding of direct sequence spread spectrum (DSSS) and Turbo code, 2-D interleaving, our newly developed resynchronization technique and incorporated with the registration technique based on motion estimation technique developed by Loo and Kinsbury, our proposed algorithm can successfully resist almost all the StirMark testing functions including both common signal processing, such as JPEG compression and median filtering, and geometric distortions. The watermarking is robust against the combination of geometric distortion and JPEG_10, the combination of large global distortion and arbitrary local small distortion. To our best knowledge, we use adaptive receiving to combat the fading of host media feature (watermark carrier) for the first time.

The problem of secure and efficient revocation of membership without incurring big costs has been considered, but no satisfactory solution was reported. In this paper, we propose a new revocation method of membership based on the ACJT group scheme. Our solution is efficient in that it only needs one multiplication and one exponentiation, which the length of exponent is fixed, to update the public key for the group manager to exclude a group member, and the signing and verifying procedure are independent of the number of current group members and excluded group members. To the best of our knowledge, the signing and verifying procedures in prior revocation schemes are dependent of the number either current group members or excluded group members, and thus the group manager needs a heavy computation load to update the public key.

A new discrete wavelet transform-based image fragile watermarking scheme exploiting the features of the human visual system is presented. Fusion of multi-resolution tamper detections, and mathe-matical morphology operations are developed for accurate tamper detection. As a result, malicious tamper and the tampered regions can be deteeted, while toleration towards high quality Iossy image compression is achieved.

The authors propose a segmentation-based hybrid image coding algorithm taking the features of the human visual system into account. A novel segmentation criterion based on luminance masking is presented. The image is segmented into blocks of different sizes and different properties. Block mean, polynomial approximation and discrete cosine transform coding are then applied to the blocks accordingly.

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.

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.