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Abstract-We present techniques for steganalysis of images that have been potentially subjected to steganographic algorithms, both within the passive warden and active warden frameworks. Our hypothesis is that steganographic schemes leave statistical evidence that can be exploited for detection with the aid of image quality features and multivariate regression analysis. To this effect image quality metrics have been identified based on the analysis of variance (ANOVA) technique as feature sets to distinguish between cover-images and stego-images. The classifier between cover and stego-images is built using multivariate regression on the selected quality metrics and is trained based on an estimate of the original image. Simulation results with the chosen feature set and wellknown watermarking and steganographic techniques indicate that our approach is able with reasonable accuracy to distinguish between cover and stego images.

Digital watermarks have been proposed in recent literature as a means for copyright protection of multimedia data. In this paper we address the capability of invisible watermarking schemes to resolve copyright ownership. We show that, in certain applications, rightful ownership cannot be resolved by current watermarking schemes alone. Specifically, we attack existing techniques by providing counterfeit watermarking schemes that can be performed on a watermarked image to allow multiple claims of rightful ownership. In the absence of standardization and specific requirements imposed on watermarking procedures, anyone can claim ownership of any watermarked image. In order to protect against the counterfeiting techniques that we develop, we examine the properties necessary for resolving ownership via invisible watermarking. We introduce and study invertibility and quasi-invertibility of invisible watermarking techniques. We propose noninvertible watermarking schemes, and subsequently give examples of techniques that we believe to be nonquasi-invertible and hence invulnerable against more sophisticated attacks proposed in the paper. The attacks and results presented in the paper, and the remedies proposed, further imply that we have to carefully reevaluate the current approaches and techniques in invisible watermarking of digital images based on application domains, and rethink the promises, applications and implications of such digital means of copyright protection. Index Terms-Attacks on digital watermarks, copyright protection, counterfeit watermarks, cryptography, invertible and noninvertible watermarking, invisible watermarks, quasi-invertible watermarking. I. INTRODUCTION T HE rapid growth of digital imagery coupled with the ease by which digital information can be duplicated and distributed has led to the need for effective copyright protection tools. Various watermarking schemes and software products have been recently introduced in attempt to address this growing concern. Given the flurry of activity that has resulted, it is natural to ask a few questions regarding all these efforts:

In this paper, we describe a class of attacks on certain block-based oblivious watermarking schemes. We show that oblivious watermarking techniques that embed information into a host image in a block-wise independent fashion are vulnerable to a counterfeiting attack. Specifically, given a watermarked image, one can forge the watermark it contains into another image without knowing the secret key used for watermark insertion and in some cases even without explicitly knowing the watermark. We demonstrate successful implementations of this attack on a few watermarking techniques that have been proposed in the literature. We also describe a possible solution to this problem of block-wise independence that makes our attack computationally intractable.

Copy-move forgery is a specific type of image tampering, where a part of the image is copied and pasted on another part of the same image. In this paper, we propose a new approach for detecting copy-move forgery in digital images, which is considerably more robust to lossy compression, scaling and rotation type of manipulations. Also, to improve the computational complexity in detecting the duplicated image regions, we propose to use the notion of counting bloom filters as an alternative to lexicographic sorting, which is a common component of most of the proposed copy-move forgery detection schemes. Our experimental results show that the proposed features can detect duplicated region in the images very accurately, even when the copied region was undergone severe image manipulations. In addition, it is observed that use of counting bloom filters offers a considerable improvement in time efficiency at the expense of a slight reduction in the robustness.

An interesting prohlem in digital forensics is that given a digital image, would it he possihle to identify the camera model which was used to obtain the image. In this paper we look at a simplified version of this problem by trying to distinguish between images captured by a limited number of camera models. We proposc i number of features which could be used by a classifier to idcntify the source camera of an image in a blind manner. We also provide experimental results and show reasonable accuracy in distinguishing images from the two and five different camera models using the proposed features.

In this work, we focus our interest on blind source camera identification problem by extending our results in the direction of [1]. The interpolation in the color surface of an image due to the use of a color filter array (CFA) forms the basis of the paper. We propose to identify the source camera of an image based on traces of the proprietary interpolation algorithm deployed by a digital camera. For this purpose, a set of image characteristics are defined and then used in conjunction with a support vector machine based multi-class classifier to determine the originating digital camera. We also provide initial results on identifying source among two and three digital cameras.