The widespread adoption of digital video techniques has generated a requirement for authenticity verification in applications such as criminal evidence, insurance claims and commercial databases. This paper extends our previous work and improves the watermark estimation procedure of a spatial digital video watermarking system designed to
detect and characterize time-base attacks. Most watermark extraction processes utilize the noise masking levels of the image. These levels change during transmission, especially when the host signal is compressed at low bit-rates. The blocking artifacts that are introduced by this process modify the noise masking levels and influence the ability to form a good estimate of the embedded watermark. This paper describes a novel filter procedure to eliminate these artifacts from the noise masking levels. The efficiency is compared with the standard MPEG-4 deblocking and deringing filters.
Extracting the watermark from only the encoded Macroblocks, excluding the skipped Macroblocks improves the performance significantly without an increase in computational complexity. The functionality of this system within an MPEG-4 implementation is demonstrated with a receiver operating characteristic.
In this paper we propose the use of a Bayesian framework to allow characterisation of image tampering from a library of attacks. We use the double watermarking strategy proposed in our previous work to derive sufficient information to drive the classifier. A non-parametric Bayesian classifier, trained on data derived from Monte
Carlo simulations is used. In addition to classification, the effects of varying the input parameters are studied. The results obtained show that the non-parametric Bayesian classifier has a very low misclassification rate for this type of problem. Explanations as to the nature of the results, and some of the practical considerations, are given.
In this paper, a new fragile watermarking system for authenticity verification is presented. This technique can detect and locate minor changes in a marked image. The method can be implemented in any domain. The embedding procedure modifies the representative value of a selected vector of coefficients according to the embedded watermark bit value. The mapping of the bits to the representative values and the formation of the orthogonal vectors are secured using a symmetric key system. The detector is a standalone system that does not need any prior knowledge about the original image or the embedded watermark. A tolerance bandwidth can be set to a minimum to reduce the level of false negative detector responses. Assuming there is a consistent pattern of tampering, an optimization algorithm has been designed to further reduce the false negative probability. By embedding the watermark in the same domain as is used for compression, the system can allow compression as an undetectable content preserving operation if the amount of quantization is known in advance. Experimental results of this system embedded in the DCT and Wavelet domain illustrate the performance and effectiveness compared with other reported fragile watermarking methods.
In this paper, we present a blind fragile authentication algorithm by modifying a robust algorithm. The embedding process modifies the relative position of one wavelet coefficient from a vector of 3 coefficients. The introduced distortion of the watermarking system is reduced by a content dependent quantization parameter. This parameter refines the quantization step according to the magnitude of the coefficients in the vector. The smallest wavelet coefficients in the smooth areas of the image are pre-distorted to improve the performance and efficiency of the algorithm in these areas. This pre-distortion does not visually degrade the image as the introduced high frequency noise is evenly distributed over these areas. A dichotomous detector compares the extracted and embedded watermark on a bit by bit basis. This results in a high detection resolution, which can deliver information about the shape of the modified object. Embedding of the watermark with a larger redundancy increases the robustness of the system to additive white Gaussian noise attack. A weighted estimation then extracts the embedded watermark. This technique is fully described in the paper. Experimental results of this system embedded in the wavelet domain illustrate the performance and effectiveness compared with other reported fragile watermarking methods.