This correspondence proposes a framework of reversible data hiding (RDH) in an encrypted JPEG bitstream. Unlike existing RDH methods for encrypted spatial-domain images, the proposed method aims at encrypting a JPEG bitstream into a properly organized structure, and embedding a secret message into the encrypted bitstream by slightly modifying the JPEG stream. We identify usable bits suitable for data hiding so that the encrypted bitstream carrying secret data can be correctly decoded. The secret message bits are encoded with error correction codes to achieve a perfect data extraction and image recovery. The encryption and embedding are controlled by encryption and embedding keys respectively. If a receiver has both keys, the secret bits can be extracted by analyzing the blocking artifacts of the neighboring blocks, and the original bitstream perfectly recovered. In case the receiver only has the encryption key, he/she can still decode the bitstream to obtain the image with good quality without extracting the hidden data.

We propose a blind identification method to estimate blur parameters of a noisy image. The noisy image is blurred and degraded due to linear motion and defocusing. In a polar coordinate system, 2D-Fourier transform of a degraded image is derived. The blur parameters are blindly estimated from the magnitude of the spectrum in the polar system, and represented on a rectangular grid. In this grid representation, vertical and horizontal projections are calculated to estimate the length and the orientation of uniform linear motion blur. As for defocus blur, only horizontal projection is used to get a blurring radius. Experimental results show that the method is accurate and computationally efficient. The estimated results are close to true values, even when the image is heavily contaminated by additive salt and pepper noise.

A robust hashing method is developed for detecting image forgery including removal, insertion, and replacement of objects, and abnormal color modification, and for locating the forged area. Both global and local features are used in forming the hash sequence. The global features are based on Zernike moments representing luminance and chrominance characteristics of the image as a whole. The local features include position and texture information of salient regions in the image. Secret keys are introduced in feature extraction and hash construction. While being robust against content-preserving image processing, the hash is sensitive to malicious tampering and, therefore, applicable to image authentication. The hash of a test image is compared with that of a reference image. When the hash distance is greater than a threshold τ1and less than τ2, the received image is judged as a fake. By decomposing the hashes, the type of image forgery and location of forged areas can be determined. Probability of collision between hashes of different images approaches zero. Experimental results are presented to show effectiveness of the method.

In visual perception, distant objects appear smaller than those close to the observer. To insert an object into an image, properly size a foreign object is difficult, especially when there is no reference object in the same distance. To detect this type of image forgery, we present a perspective-constraint based method, with which the height ratio of two objects in an image can be determined without any knowledge of the camera parameters. Assuming that the camera is held leveled and with negligible tilt, the height ratio can be found merely by a vanishing line of the plane on which both objects of interest is situated. Once the estimated ratio exceeds a tolerable interval, a forged region is identified. Experimental results show efficacy of the method even if the images to be tested have been down-sampled or compressed with a low quality factor.

Structural image features are exploited to construct perceptual image hashes in this work. The image is first preprocessed and divided into overlapped blocks. Correlation between each image block and a reference pattern is calculated. The intermediate hash is obtained from the correlation coefficients. These coefficients are finally mapped to the interval [0, 100], and scrambled to generate the hash sequence. A key component of the hashing method is a specially defined similarity metric to measure the “distance” between hashes. This similarity metric is sensitive to visually unacceptable alterations in small regions of the image, enabling the detection of small area tampering in the image. The hash is robust against content-preserving processing such as JPEG compression, moderate noise contamination, watermark embedding, re-scaling, brightness and contrast adjustment, and low-pass filtering. It has very low collision probability. Experiments are conducted to show performance of the proposed method.

Region duplication is a common type of digital image tampering. This paper presents a log-polar based approach to detect such forgery even if the copied area has been rotated and/or scaled. We compute log-polar fast Fourier transform (LPFFT) on image blocks to approximate the log-polar Fourier transform (LPFT). LPFFT is based on a nearly log-polar system where conversion to log-polar coordinates only involves 1-D Fourier transform and interpolation operations. In addition to rotation and scaling invariance, computation complexity of LPFFT isO(n2logn) , much lower thanO(n4) of LPFT whennis large. Similarity of the LPFFT results between different blocks provides indication of image tampering. Experimental results show efficacy of the proposed method.

This paper proposes two novel self-embedding watermarking schemes based upon a reference sharing mechanism, in which the watermark to be embedded is a reference derived from the original principal content in different regions and shared by these regions for content restoration. After identifying tampered blocks, both the reference data and the original content in the reserved area are used to recover the principal content in the tampered area. By using the first scheme, the original data in five most significant bit layers of a cover image can be recovered and the original watermarked image can also be retrieved when the content replacement is not too extensive. In the second scheme, the host content is decomposed into three levels, and the reference sharing methods with different restoration capabilities are employed to protect the data at different levels. Therefore, the lower the tampering rate, the more levels of content data are recovered, and the better the quality of restored results.

Motivated by the image rescaling estimation method proposed by Gallagher (2nd Canadian Conf. Computer & Robot Vision, 2005: 65-72), we develop an image rotation angle estimator based on the relations between the rotation angle and the frequencies at which peaks due to interpolation occur in the spectrum of the image's edge map. We then use rescaling/rotation detection and parameter estimation to detect fake objects inserted into images. When a forged image contains areas from different sources, or from another part of the same image, rescaling and/or rotation are often involved. In these geometric operations, interpolation is a necessary step. By dividing the image into blocks, detecting traces of rescaling and rotation in each block, and estimating the parameters, we can effectively reveal the forged areas in an image that have been rescaled and/or rotated. If multiple geometrical operations are involved, different processing sequences, i.e., repeated zooming, repeated rotation, rotation-zooming, or zooming-rotation, may be determined from different behaviors of the peaks due to rescaling and rotation. This may also provide a useful clue to image authentication.

High-performance steganography requires large embedding rate and small distortion, i.e., high embedding efficiency. Steganographic codes (stego-codes) derived from covering codes can improve embedding efficiency. In this paper, a new method is proposed to construct binary stego-codes for LSB embedding in gray-scale signals, which shows that not just one but a family of stego-codes can be generated from a covering code by combining Hamming codes and wet paper codes. This method can greatly expand the set of embedding schemes as applied to steganography. Performances of stego-code families (SCF) of structured codes and random codes are analyzed. SCFs of random codes can approach the rate-distortion bound on LSB embedding for any chosen embedding rate. Furthermore, SCFs are modified for applications in±1embedding, and a treble layered embedding method for±2embedding is obtained. By combining the modified SCFs and the treble layered method, a near-optimal scheme for±2embedding is presented.

This letter proposes a novel multibit assignment steganography for palette images, in which each gregarious color that possesses close neighboring colors in the palette is exploited to represent several secret bits. A method for producing a usable multibit assignment is presented. For any pixel with a gregarious color, a data-hider can always find a suitable neighbor of the original color that corresponds to a prefix of secret bit-sequence and then replaces the original color with the found neighboring color. Experiment results show that the proposed steganography provides a good payload-distortion performance.

This paper proposes a novel fragile watermarking scheme capable of perfectly recovering the original image from its tampered version. In the scheme, a tailor-made watermark consisting of reference-bits and check-bits is embedded into the host image using a lossless data hiding method. On the receiver side, by comparing the extracted and calculated check-bits, one can identify the tampered image-blocks. Then, the reliable reference-bits extracted from other blocks are used to exactly reconstruct the original image. Although content replacement may destroy a portion of the embedded watermark data, as long as the tampered area is not too extensive, the original image information can be restored without any error.

In sensitivity attacks, attempts across the boundary between "watermarked" and "not watermarked" using an available detector can provide adequate information about an embedded watermark for clearing it without causing serious distortion. This letter proposes a novel watermarking system capable of resisting such sensitivity attacks, which contains a tailor-made embedding algorithm and a corresponding detecting method. Although an attacker can still find the most effective way for destroying the watermark in a constructed signal near the boundary, it is impossible to move a watermarked product away from the "watermarked" region with low distortion. Therefore, the watermark detector can be widely distributed without fear of being used for sensitivity attacks

Capability of accurately locating tampered pixels is desirable in image authentication. We propose a novel statistical scheme of fragile watermarking, in which a set of tailor-made authentication data for each pixel together with some additional test data are embedded into the host image. On the authentication side, examining the pixels and their corresponding authentication data will reveal the exact pattern of the content modification. As long as the tampered area is not too extensive, two distinct probability distributions corresponding to tampered and original pixels can be used to exactly identify the tampered pixels.

In image steganography, a pixel can carry secret bits by choosing adding/subtracting one to/from the gray value. This kind of "plusmn1 steganography" can hide a longer message than simple LSB embedding. We propose a double-layered embedding method for implementing "plusmn1 steganography," in which binary covering codes and wet paper codes are used to hide messages in the LSB plane and the second LSB plane, respectively. We show that this method can achieve the upper bound on the embedding efficiency of "plusmn1 steganography" when the employed binary covering codes reach the upper bound on that of LSB steganography. Applications using random and structured covering codes show that the new method outperforms previous ones and can approach the upper bound.

A copyright management system for online trade of digital images is proposed in which low-resolution images with a visible mark are freely downloadable. An authorized user receives a package containing the details of the image he/she buys together with a key for mark removing. Using a downloaded client-end routine, the user removes the mark, reconstructs the high-quality image and embeds a robust fingerprint in the image simultaneously.

An iterative image resolution enhancement algorithm is presented based on a Bayesian MAP estimator. In order to speed up convergence and improve stability, additive regularization terms based on a set of exponentially varying weights and a least square criterion are added to the cost functional. Experimental results show that sufficient numbers of low-resolution frames and iterations are needed to produce a high-resolution image. However, excessive frames and iterations do not provide further improvement of the reconstructed image quality

An active warden can significantly reduce the steganographic information capacity by slightly modifying some contents of suspected media. When using QIM-based embedding methods, the steganographic capacity in the presence of active attack can be obtained with a secure transform, an identical suitable quantization step and a corresponding length of embedded bits. It is shown that the maximum attainable payload is determined by the size of cover media and the ratio between distortion levels caused by the data-hider and the active warden respectively.

A novel coding method for digital steganography is described, in which the amount of bit alterations introduced into a cover medium is significantly reduced, leading to less distortion and enhanced security against steganalysis. Unlike other block-based stego-coding approaches, the proposed method works in a running manner. In this way, each secret bit is represented by a series of consecutive cover bits, and flipping of one cover bit can be used to insert several secret bits. Theoretical analysis shows that, by reducing host alterations and inducing less distortion, the running coding has advantages over a previous technique.

This letter proposes a novel steganographic scheme that employs human vision sensitivity to hide a large amount of secret bits into a still image with a high imperceptibility. In this method, data to be embedded are converted into a series of symbols in a notation system with multiple bases. The specific bases used are determined by the degree of local variation of the pixel magnitudes in the host image so that pixels in busy areas can potentially carry more hidden data. Experimental results are given to show the advantage of this adaptive technique.