In this paper, we propose a semi-fragile watermarking technique that accepts JPEG lossy compression on the watermarked image to a pre-determined quality factor, and rejects malicious attacks. The authenticator can identify the positions of corrupted blocks, and recover them with approximation of the original ones. In addition to JPEG compression, adjustments of the brightness of the image within reasonable ranges, are also acceptable using the proposed authenticator. The security of the proposed method is achieved by using the secret block mapping function which controls the signature generating/embedding processes. Our authenticator is based on two invariant properties of DCT coecients before and after JPEG compressions. They are deterministic so that no probabilistic decision is needed in the system. The first property shows that if we modify a DCT coecient to an integral multiple of a quantization step, which is larger than the steps used in later JPEG compressions, then this coecient can be exactly reconstructed after later acceptable JPEG compression. The second one is the invariant relationships between two coecients in a block pair before and after JPEG compression. Therefore, we can use the second property to generate authentication signature, and use the first property to embed it as watermarks. There is no perceptible degradation between the watermarked image and the origianl. In additional to authentication signatures, we can also embed the recovery bits for recovering approximate pixel values in corrupted areas. Our authenticator utilizes the compressed bitstream, and thus avoids rounding errors in reconstructing DCT coecients. Experimental results showed the effectiveness of this system. The system also guarantees no false alarms, i.e., no acceptable JPEG comp...

The existing digital data verification methods are able to detect regions that have been tampered with, but are too fragile to resist incidental manipulations. This paper proposes a new digital signature scheme which makes use of an image's contents (in the wavelet transform domain) to construct a structural digital signature (SDS) for image authentication. The characteristic of the SDS is that it can tolerate content-preserving modifications while detecting content-changing modifications. Many incidental manipulations, which were detected as malicious modifications in the previous digital signature verification or fragile watermarking schemes, can be bypassed in the proposed scheme. Performance analysis is conducted and experimental results show that the new scheme is indeed superb for image authentication. keywords: Digital signature, Wavelet transform, Authentication, Fragility, Robustness. The preliminary version of this paper will be published in [14] (http://smart.iis.sinica.ed...

Many image watermarks have been proposed to protect intellectual property in an age where digital images may be easily modified and perfectly reproduced. In a fragile marking system, a signal (watermark) is embedded within an image such that subsequent alterations to the watermarked image can be detected with high probability. The insertion of the watermark is perceptually invisible under normal human observation. These types of marks have found applicability in image authentication systems. In this paper we discuss fragile marking systems and their desirable features, common methods of attack, and survey some recent marking systems.

We propose a novel multipurpose watermarking scheme, in which robust and fragile watermarks are simultaneously embedded, for copyright protection and content authentication. By quantizing a host image's wavelet coefficients as masking threshold units (MTUs), two complementary watermarks are embedded using cocktail watermarking and they can be blindly extracted without access to the host image. For the purpose of image protection, the new scheme guarantees that, no matter what kind of attack is encountered, at least one watermark can survive well. On the other hand, for the purpose of image authentication, our approach can locate the part of the image that has been changed and tolerate some incidental processes that have been executed. Experimental results show that the performance of our multipurpose watermarking scheme is indeed superb in terms of robustness and fragility. Keywords: Robust watermarking, Copyright protection, Fragile watermarking, Authentication. 1 1 Introduction C...

Image authentication verifies the originality of an image by detecting malicious manipulations. This goal is different from that of image watermarking which embeds into the image a signature surviving most manipulations. Existing methods for image authentication treat all types of manipulation equally (i.e., as unacceptable). However, some applications demand techniques that can distinguish acceptable manipulations (e.g., compression) from malicious ones. In this paper, we describe an effective technique for image authentication which can prevent malicious manipulations but allow JPEG lossy compression. The authentication signature is based on the invariance of the relationship between DCT coefficients of the same position in separate blocks of an image. This relationship will be preserved when these coefficients are quantized in a JPEG compression process. Our proposed method can distinguish malicious manipulations from JPEG lossy compression regardless of how high the compression ratio is. We also show that, in different practical cases, the design of authenticator depends on the number of recompression times and on whether the image is decoded into integral values in the pixel domain during the recompression process. Theoretical and experimental results indicate that this technique is effective for image authentication.

In this paper, we describe some weaknesses of public-key blockwise fragile authentication water-markings and the means to make them secure. Wong’s original algorithm as well as a number of its variant techniques are not secure against a mere block cut-and-paste or the well-known birthday attack. To make them secure, some schemes have been proposed to make the signature of each block depend on the contents of its neighbouring blocks. We attempt to maximise the change local-isation resolution using only one dependency per block with a scheme we call hash block chaining version 1 (HBC1). We then show that HBC1, as well as any neighbour content-dependent scheme, are susceptible to another forgery technique that we have named a transplantation attack. We also show a new kind of birthday attack that can be effectively mounted against HBC1. To thwart these attacks, we propose using a nondeterministic digital signature together with a signature-dependent scheme (HBC2). Finally, we discuss the advantages of using discrete logarithm signatures instead of RSA for watermarking. 1.

Digital image manipulation software is now readily available on personal computers. It is therefore very simple to tamper with any image and make it available to others. Insuring digital image integrity becomes a major issue. In this paper, we propose an original method to protect image authenticity using an invisible and robust watermark. Our scheme is independent of the signer, however the latter must have a high capacity and be able to extract the watermark in full blind detection mode. Our approach is based on the extraction of features from the image. These features are chosen so as to be unaffected by non malicious alterations such as lossy compression. They are embedded in the image using an iterative process so that watermarked image features and information contained in the watermark coincide perfectly. The authenticity is verified by comparing the features of the tested image, with those of the original image recovered from the watermark. 1. Introduction Digital image manip...

Blind or oblivious data hiding, can be considered as a signaling method where the origin of the signal constellation is not known. The origin however, can be estimated, by means of self-noise suppression techniques. In this paper, we propose such a technique, and present both theoretical and numerical evaluations of its performance in an additive noise scenario. The problem of optimal choice of the parameters of the proposed technique is also explored, and solutions are presented. Though the cover object is assumed to be an image for purposes of illustration, the proposed method is equally applicable for other types of multimedia data, like video, speech or music.

The recent explosion in shared media content and sensed data produced by mobile end-users is challenging well-established principles and assumptions in data trust models. A fundamental issue we address in this paper is how to establish some trust level in the authenticity of content created by untrusted mobile users. We advocate a secure localization and certification service that allows content producers to tag their content with with a spatial timestamp indicating its physical location. At the same time, however, our approach preserves the privacy of producers by not exposing their identity to the potential content consumers. We provide a list of existing and possible applications that would profit from such a secure localization service and sketch possible implementations of the service, highlighting advantages and drawbacks. 1.

Digital watermarking appears today as an e cient mean of securing multimedia documents. Several application scenarios in the security of digital watermarking have been pointed out, each of them with di erent requirements. The three main identi ed scenarios are: copyright protection, i.e. protecting ownership and usage rights; tamper proo ng, aiming at detecting malicious modi cations; and authentication, the purpose of which is to check the authenticity of the originator of a document. While robust watermarks, which survive to any change or alteration of the protected documents, are typically used for copyright protection, tamper proo ng and authentication generally require fragile or semi-fragile watermarks in order to detect modi ed or faked documents. Further, most of robust watermarking schemes are vulnerable to the so-called copy attack, where a watermark can be copied from one document to another by any unauthorized person, making these schemes ine cient in all authentication applications. In this paper, we propose a hybrid watermarking method joining a robust and a fragile or semi-fragile watermark, and thus combining copyright protection and tamper proo ng. As a result this approach is at the same time resistant against copy attack. In addition, the fragile information is inserted in a way which preserves robustness and reliability of the robust part. The numerous tests and the results obtained according to the Stirmark benchmark demonstrate the superior performance of the proposed approach.