We propose an asymmetric fragile watermarking technique that uses a number theoretic transform (NTT). Signature data is extracted from a watermarked image by determining correlation functions that are computed using the NTT. The effectiveness of the proposed method is evaluated by simulated detection of altering.

In this study, we propose a complete architecture based on digital watermarking techniques to solve the issue of copyright protection and authentication for digital contents. We apply visible and semi-fragile watermarks as dual watermarks where visible watermarking is used to establish the copyright protection and semi-fragile watermarking authenticates and verifies the integrity of the watermarked image. In order to get the best tradeoff between the embedding energy of watermark and the perceptual translucence for visible watermark, the composite coefficients using global and local characteristics of the host and watermark images in the discrete wavelet transform (DWT) domain is considered with Human Vision System (HVS) models. To achieve the optimum noise reduction of the visibility thresholds for HVS in DWT domain, the contrast-sensitive function (CSF) and noise visible function (NVF) of perceptual model is applied which characterizes the global and local image properties and identifies texture and edge regions to determine the optimal watermark locations and strength at the watermark embedding stage. In addition, the perceptual weights according to the basis function amplitudes of DWT coefficients is fine tuned for the best quality of perceptual translucence in the design of the proposed watermarking algorithm. Furthermore, the semi-fragile watermark can detect and localize malicious attack effectively yet tolerate mild modifications such as JPEG compression and channel additive white Gaussian noise (AWGN). From the experimental results, our proposed technique not only improves the PSNR values and visual quality than other algorithms but also preserves the visibility of the watermark visible under various signal processing and advanced image recovery attacks.

In this study, a novel binary image authentication scheme is proposed, which can be used to detect any alteration of the host image. In the proposed scheme, the watermark is embedded into a host image using a Hamming-code-based embedding algorithm. A performance analysis shows that the proposed scheme achieves both smaller distortion and lower false negative rates than the previous schemes.

In this paper, we propose a new fragile watermarking scheme that can be used to verify three-dimensional (3-D) polygonal models by detecting unauthorized alterations. In order to generate a binary watermark sequence, we combine a binary random sequence generated by the user key with a binary logo sequence using the bit-wise exclusive OR operation. The binary watermark sequence is embedded into 3-D triangle strips by perturbing their vertex coordinates. The proposed watermarking scheme can identify specific locations that have been changed. Changes of the vertex coordinates in the watermarked 3-D model are reflected in the extracted watermark image, which indicates the attacked area. Experimental results demonstrate that we can detect various modifications of the watermarked 3-D model: translation, rotation, scaling, randomization of points, polygon simplification, geometry compression, and local deformation.

Conventional authentication methods, proposed mainly for gray-scale and color images, are not appropriate for palette images, which usually contain simple contents with a limited number of colors. In this paper, a new approach is proposed to verify the integrity of palette images and to locate tampered regions without re-quantization and re-indexing processes. The proposed approach is based on a combined use of both the fragile watermarking and the digital signature approaches, taking the advantages of both approaches and avoiding their drawbacks. To protect a block of an image, authentication signals are first generated according to a secret key. Based on an embeddability property defined in the study, the pixels of each block are classified as embeddable or non-embeddable. Only the former ones are used to embed the authentication signals. A corresponding digital signature is generated as well to compensate the possibly limited embedding capacity of the embeddable pixels that are insufficient in number. To authenticate a block, the recovered authentication signals, yielded from the extracted watermark and the received digital signature, are compared with the one generated according to the correct secret key, to prove the block's legitimacy. The effectiveness and the security of the proposed method are analyzed and tested with a variety of palette images. The results indicate that the proposed method can offer high authentication accuracy as well as maintain a good tradeoff between the authentication signal portability and the resulting image quality.