A. V. Subramanyam

Robust Watermarking of Compressed and Encrypted JPEG2000 Images

Digital asset management systems (DAMS) generally handle media data in a compressed and encrypted form. It is sometimes necessary to watermark these compressed encrypted media items in the compressed-encrypted domain itself for tamper detection or ownership declaration or copyright management purposes. It is a challenge to watermark these compressed encrypted streams as the compression process would have packed the information of raw media into a low number of bits and encryption would have randomized the compressed bit stream. Attempting to watermark such a randomized bit stream can cause a dramatic degradation of the media quality. Thus it is necessary to choose an encryption scheme that is both secure and will allow watermarking in a predictable manner in the compressed encrypted domain. In this paper, we propose a robust watermarking algorithm to watermark JPEG2000 compressed and encrypted images. The encryption algorithm we propose to use is a stream cipher. While the proposed technique embeds watermark in the compressed-encrypted domain, the extraction of watermark can be done in the decrypted domain. We investigate in detail the embedding capacity, robustness, perceptual quality and security of the proposed algorithm, using these watermarking schemes: Spread Spectrum (SS), Scalar Costa Scheme Quantization Index Modulation (SCS-QIM), and Rational Dither Modulation (RDM).

Video forgery detection using HOG features and compression properties

In this paper, we propose a novel video forgery detection technique to detect the spatial and temporal copy paste tampering. It is a challenge to detect the spatial and temporal copy-paste tampering in videos as the forged patch may drastically vary in terms of size, compression rate and compression type (I, B or P) or other changes such as scaling and filtering. In our proposed algorithm, the copy-paste forgery detection is based on Histogram of Oriented Gradients (HOG) feature matching and video compression properties. The benefit of using HOG features is that they are robust against various signal processing manipulations. The experimental results show that the forgery detection performance is very effective. We also compare our results against a popular copy-paste forgery detection algorithm. In addition, we analyze the experimental results for different forged patch sizes under varying degree of modifications such as compression, scaling and filtering.

Compression noise based video forgery detection

Intelligent video editing techniques can be used to tamper videos such as surveillance camera videos, defeating their potential to be used as evidence in a court of law. In this paper, we propose a technique to detect forgery in MPEG videos by analyzing the frames compression noise characteristics. The compression noise is extracted from spatial domain by using a modified Huber Markov Random Field (HMRF) as a prior for image. The transition probability matrices of the extracted noise are used as features to classify a given video as single compressed or double compressed. The experiment is conducted on different YUV sequences with different scale factors. The efficiency of our classification is observed to be higher relative to the state of the art detection algorithms.

Compressed-encrypted domain JPEG2000 image watermarking

In digital rights management (DRM) systems, digital media is often distributed by multiple levels of distributors in a compressed and encrypted format. The distributors in the chain face the problem of embedding their watermark in compressed, encrypted domain for copyright violation detection purpose. In this paper, we propose a robust watermark embedding technique for JPEG2000 compressed and encrypted images. While the proposed technique embeds watermark in the compressed-encrypted domain, the extraction of watermark can be done either in decrypted domain or in encrypted domain.

Pixel estimation based video forgery detection

In this paper, we propose a novel technique to detect double quantization, which results due to double compression of a tampered video. The proposed algorithm uses principles of estimation theory to detect double quantization. Each pixel of a given frame is estimated from the spatially colocated pixels of all the other frames in a Group of Picture (GOP). The error between the true and estimated value is subjected to a threshold to identify the double compressed frame or frames in a GOP. The advantage of this algorithm is that it can detect tampering of I, P or B frames in a GOP with high accuracy. In addition, the technique can also detect forgery under wide range of double compression bitrates or quantization scale factors. We compare our experimental results against popular video forgery detection techniques and establish the effectiveness of the proposed technique.

Sensor Pattern Noise Estimation Using Probabilistically Estimated RAW Values

Photo response nonuniformity (PRNU) is consider as reliable camera fingerprint for identifying source of a digital images. Digital cameras use various image processing operations to map linear color measurements (raw data) into nonlinear narrow gamut image. This nonlinear transformation affects estimation of PRNU. To undo the effect of nonlinear transformation, in this letter, we propose to estimate PRNU from probabilistically obtained raw values. Since not all cameras provide raw values as their output, we propose to compute estimate of raw values from the JPEG images using probabilistic color derendering procedure. The estimated raw values are modeled as a Poisson process and then maximum likelihood estimation (MLE) is used for PRNU estimation. The experimental results show that, the digital camera identification using our proposed PRNU estimate is better than using other popular PRNU estimate.

ACE–An Effective Anti-forensic Contrast Enhancement Technique

Detecting Contrast Enhancement (CE) in images and anti-forensic approaches against such detectors have gained much attention in multimedia forensics lately. Several contrast enhancement detectors analyze the first order statistics such as gray-level histogram of images to determine whether an image is CE or not. In order to counter these detectors various anti-forensic techniques have been proposed. This led to a technique that utilized second order statistics of images for CE detection. In this letter, we propose an effective anti-forensic approach that performs CE without significant distortion in both the first and second order statistics of the enhanced image. We formulate an optimization problem using a variant of the well known Total Variation (TV) norm image restoration formulation. Experiments show that the algorithm effectively overcomes the first and second order statistics based detectors without loss in quality of the enhanced image.

Audio watermarking in partially compressed-encrypted domain

In Digital Asset Management systems, media is often handled in compressed and encrypted form. In this paper, we propose a novel partially compressed-encrypted robust MP3 audio watermarking technique. However, arbitrary embedding of a watermark in a partially compressed encrypted MP3 audio can cause drastic degradation of the quality as the underlying change may result in random decrypted values. In addition, encryption may result in very low compression efficiency. Thus the challenge is to design a watermarking technique that provides good watermarked audio quality and at the same time gives good compression efficiency. While the proposed technique embeds watermark in the partially compressed-encrypted domain, the extraction of watermark can be done in the encrypted or decrypted domains. The experiments show that the watermarked audio quality is good and the reduction in compression efficiency is low. The experimental results also show that the proposed watermarking technique is robust to common signal processing attacks.

Spatial domain quantization noise based image filtering detection

Smart image editing and processing techniques make it easier to manipulate an image convincingly and also hide any artifacts of tampering. Common real world forgeries can be accompanied by enhancement operations like filtering, compression and/or format conversion to suppress forgery artifacts. Out of these enhancement operations, filtering is very common and has received a lot of attention in forensics research lately. However, different filtering operations and image formats are not investigated deeply and simultaneously. We propose an algorithm to detect if a given image has undergone filtering based enhancement irrespective of the format of image or the type of filter applied. In the proposed algorithm, we exploit the correlation of spatial domain quantization noise of an image by extracting transition probability features and classify the image as filtered or unfiltered. Experiments are performed to evaluate the robustness and compare the performance of the proposed technique with popular forensic filtering detection algorithms and is found to be superior in most of the cases.

Partially compressed-encrypted domain robust JPEG image watermarking

Digital media is often handled in a compressed and encrypted form in Digital Asset Management Systems. And watermarking of the compressed encrypted media items in the compressed-encrypted domain itself is required sometimes for copyright violation detection or other purposes. In this paper, we propose a robust image watermarking technique for partially compressed-encrypted JPEG images. However, arbitrary embedding of a watermark in a partially compressed encrypted image can cause drastic degradation of the quality as the underlying change may result in random decrypted values. In addition, due to the encryption the compression efficiency may become very low. Thus the challenge is to design a watermarking technique that provides good watermarked image quality and at the same time gives good compression efficiency. While the proposed technique embeds watermark in the partially compressed-encrypted domain, the extraction of watermark can be done in the encrypted or decrypted domains. The experiments show that the watermarked image quality is good and the reduction in compression efficiency is low. The proposed watermarking technique is robust to common signal processing attacks. The watermark detection performance of the proposed scheme is better than the existing encrypted domain watermarking techniques.