Yaoran Huo

A semi-fragile image watermarking algorithm with two-stage detection

The ability against the collage attack of semi-fragile watermarking is improved by embedding the watermark of a block in other blocks, but the tamper detection performance is impaired under general tampering. A two-stage detection method is proposed to improve the tamper detection performance of semi-fragile watermarking. For each 8 × 8 block, six-bit watermark data generated by the significant DCT (Discrete Cosine Transformation) coefficients are divided into two parts with the same length: general tampering watermark (GTW) and collage attack watermark (CAW). The GTW and CAW data of a block are embedded in the quantized DCT coefficients of itself and other blocks, respectively. In the first-stage detection, the general tampered regions are localized by the GTW data. To identify whether the collage attack exists in the received image, the identification parameter is defined by both GTW and CAW data. The selection of the predefined threshold of the identification parameter is derived and verified by the statistical experiments. If the identification parameter is larger than the given threshold, the second stage detection is performed to detect the collaged regions. Experimental results demonstrate that the proposed two-stage detection method is able to identify tampering with high probability under general tampering, collage attack and hybrid attack.

Compressive adaptive ghost imaging via sharing mechanism and fellow relationship

For lower sampling rate and better imaging quality, a compressive adaptive ghost imaging is proposed by adopting the sharing mechanism and fellow relationship in the wavelet tree. The sharing mechanisms, including intrascale and interscale sharing mechanisms, and fellow relationship are excavated from the wavelet tree and utilized for sampling. The shared coefficients, which are part of the approximation subband, are localized according to the parent coefficients and sampled based on the interscale sharing mechanism and fellow relationship. The sampling rate can be reduced owing to the fact that some shared coefficients can be calculated by adopting the parent coefficients and the sampled sum of shared coefficients. According to the shared coefficients and parent coefficients, the proposed method predicts the positions of significant coefficients and samples them based on the intrascale sharing mechanism. The ghost image, reconstructed by the significant coefficients and the coarse image at the given largest scale, achieves better quality because the significant coefficients contain more detailed information. The simulations demonstrate that the proposed method improves the imaging quality at the same sampling rate and also achieves a lower sampling rate for the same imaging quality for different types of target object images in noise-free and noisy environments.

Self-recovery fragile watermarking scheme with variable watermark payload

To take into account security, invisibility and recovery quality, this work proposes a variable-payload self-recovery fragile watermarking scheme. For each block, the watermarks include the total-watermark with variable number of bits and the basic-watermark of length 24 bits. The two watermark versions of each block are embedded into the less significant bit planes of the different blocks based on the secret key, respectively. They not only can partially resolve the coincidence tampering problem, but also improve the performance of tamper detection. The variable watermark payload preserves the adequate information of image block to as few bits as possible. Simulation results demonstrate that the proposed scheme not only provides a better invisibility and security against the known counterfeiting attacks, but also allows image recovery with an acceptable visual quality up to 60% tampering.

Self-embedding watermarking scheme against JPEG compression with superior imperceptibility

To improve the imperceptibility, security and tamper detection performance, a self-embedding watermarking scheme against JPEG compression is proposed in this work. The recovery watermark of all blocks in the host image, which consists of 6-bit DC-code and 5-bit AC-code and simultaneously used to both tamper detection and tamper recovery, is recombined based on the secret key and embedded in the quantized DCT coefficients. This strategy not only enhances the ability against the known forgery attacks due to introducing multi-blocks independency, but also improves the tamper detection performance by designing the tamper detection method based on the multi-neighbor characteristic and multi-threshold optimization. To achieve the better imperceptibility, the 7 middle frequency DCT coefficients of an 8 × 8 block are chosen to hide the 11-bit watermark by adopting the weight-function modulo based embedding method. Robustness against JPEG compression is enhanced by setting the quantization step of the chosen DCT coefficients according to the standard JPEG quantization table and an adjustable scaling factor which balances the robustness with imperceptibility. We also discuss the effects of different scaling factors on the imperceptibility and robustness in terms of peak signal to noise ratio (PSNR) and survival quality factor (SQF) of watermarked image generated by a given scaling factor. Experimental results demonstrate that the proposed method outperforms conventional semi-fragile restorable watermarking schemes in imperceptibility, tamper detection and tamper recovery in various forgery attacks especially for JPEG compression with low QFs.

A Restorable Semi-fragile Watermarking Combined DCT with Interpolation

In this paper, a semi-fragile watermarking with interpolation method is proposed to improve recovery performance with less recovery watermark capacity. The original image is 2-fold down sampled to reduce the watermark payload and DCT (Discrete Cosine Transformation) is calculated on each 4 × 4 block in the down-sampled image. The DC coefficient and first two AC coefficients in each 4 × 4 block are quantized by selected quantized steps respectively and encoded with 11 bits to generate the recovery watermark corresponding to 8 × 8 block in the original image. The recovery watermark of each 8 × 8 block is embedded in the quantized DCT coefficients of other blocks. At the recovery side, the low resolution image is firstly reconstructed by the extracted valid recovery watermark and the high resolution one is reconstructed by the interpolation method based on the low resolution one. The tampered blocks are recovered by the corresponding blocks in the high resolution image. The image inpainting method is also used to recover the tampering coincident blocks. Experimental results show that the proposed restorable semi-fragile watermarking method can achieve better recovery performance under JPEG (Joint Photographic Experts Group) compression with superior invisibility.

Self-embedding fragile watermarking scheme combined average with VQ encoding

Combined average encoding with vector quantization (VQ) encoding, a new self-embedding fragile watermarking scheme is proposed. To take into account watermark payload, localization accuracy and recovery quality, the 6-bit average-watermark of a 2×2 original block and the 8-bit VQ-watermark of a 4×4 block of image high-frequency component are generated and hidden in the corresponding mapping blocks of them based on secret key, respectively. To improve the tamper detection performance, the validity of a 2×2 block is determined by combining the average-watermark with the VQ-watermark. The average, VQ and inpainting recovery operations are executed in sequence to improve the recovery quality especially for a larger tampering ratio. Simulation results demonstrate that the proposed scheme not only provides a better invisibility and security against the known counterfeiting attacks, but also allows image recovery with an acceptable visual quality up to 70% tampering ratios.

An alterable-capacity authentication watermarking algorithm with superior localization

To meet different security demands, this work proposes an alterable-capacity algorithm for JPEG images. First, the original image is divided into 8×8 blocks. The authentication watermarks of each block are computed by its quantized DCT coefficients and the secret-matrix generated by user key, where the size of secret-matrix depends on the watermark capacity. The authentication watermarks of each block are embedded into the middle quantized DCT coefficients in other blocks. The validity of the test block is determined by comparing the number of inconsistent blocks in eight neighbor blocks of test block with the average of that of its mapping blocks. To further enhance the performance of tamper detection, the invalid block will be set valid if there are three and less invalid blocks in its eight neighbor blocks. We also discuss that the interaction among watermark capacity, invisibility and tamper detection performance. Experimental results show that the proposed scheme outperforms the literature [8] in tamper detection with the same watermark capacity.

A restorable fragile watermarking scheme with superior localization for both natural and text images

In this paper, we present a method for detecting and restoring tampered information in natural and text images. To take the detection ability, invisibility, and recovery quality into account for both natural and text images, this work generates the authentication watermark for each 4 × 4 block by a hash function and a variable capacity recovery watermark for each 2 × 2 block by allocating more bits to the textural blocks and fewer bits to the smooth ones. The authentication watermark and the recovery one are embedded in the original image by adopting different strategies based on a secret key. The multi-stage neighbor detection strategy is designed to locate the tampered image blocks accurately. The proposed scheme outperforms in invisibility, with detecting tampered locations and recovery of the tampered regions. The simulation results show that the proposed scheme achieves better recovery quality and invisibility for natural and text images due to a variable-capacity recovery watermark and superior localization. Further, the proposed method computationally is less expensive compared with the existing works.

Semi-fragile watermarking scheme with discriminating general tampering from collage attack

A semi-fragile watermarking scheme is proposed to discriminate general tampering and collage attack in this paper. Five bits watermark data of each block generated are divided into the general tampering watermark (GTW) and collage attack watermark (CAW), which are embedded in the same block and the other blocks to discriminate general tampering and collage attack. The general tampered regions are obtained by the GTW data, and used to define a new collage identification parameter (CIP) combined with the consistency mark of collage attack. If the CIP is less than the given threshold, there are collaged regions in the test image and the CAW data is used to localize the collaged region. This work also discusses the selection of threshold of CIP. Experimental results show that the proposed algorithm improves the tamper detection performance compared to the existing semi-fragile watermarking algorithms and has the ability to discriminate general tampering from collage attack.