A data embedding method is proposed for image authentication based on table look-up in frequency domain. A visually meaningful watermark and a set of simple features are embedded invisibly in the marked image, which can be stored in the compressed form. The scheme can detect and localize alterations of the original image, such as the tempering of images exported from a digital camera. Keywords: digital watermark, image authentication. 1. INTRODUCTION Digital information revolution has brought about many advantages and new issues. With the ease of editing and perfect reproduction, the protection of ownership and the prevention of unauthorized manipulation of digital audio, image, and video materials become important concerns. Digital watermarking, a scheme to embed special labels in digital sources, has made considerable progress in recent years. There are several categories of watermarking schemes [1]. Among them, fragile watermarking is a technique to insert a signature for image ...

images, videos or audio les easy. While this enables numerous new applications, a certain loss of trust in digital media can be observed. In general, there is no guarantee that a digital image \does not lie", i.e., that the image content was not altered. To counteract this risk, fragile watermarks were proposed to protect the integrity of digital multimedia objects. In high security applications, it is necessary to be able to reconstruct the original object out of the watermarked version. This can be achieved by the use of invertible watermarks. While traditional watermarking schemes introduce some small non-invertible distortion in the digital content, invertible watermarks can be completely removed from a watermarked work. In the past, the security of proposed image authentication schemes based on invertible watermarks was only analyzed using ad-hoc methods and neglected the possibility of malicious attacks, which aim at engineering a fake mark so that the attacked object appears to be genuine. In this paper, we characterize and analyze possible malicious attacks against watermark-based image authentication systems and explore the theoretical limits of previous constructions with respect to their security.