An Invisible Watermarking Technique for Image Verification

In this papel; we propose a new method for invisibly watermarking high-quality color and gray-scale images. This method is intendedfor use in image ver$cation applications, where one is interested in knowing whether the content of an image has been altered since some earlier time, perhaps because of the act of a malicious party. It consists of both a watermark stamping process which embeds a watermark in a source image, and a watermark extraction process which extracts a Watermark from a stamped image. The extracted watermark can be used to determine whether the image has been altered. The processing used in the stamping and extraction processes is presented in the papel: We also discuss some advantages of this technique over other invisible watermarking techniques for the veri$cation application; these include a high degree of invisibility, color preservation, ease of decoding, and a high degree of protection against retention of the Watermark after unauthorized alterations. nipulation of the least significant bit (LSB). Walton[3] described techniques to embed long strings of binary bits at a set of randomly generated addresses where the LSB of pixels were changed to match the corresponding bit in the string. The watermarking techniques in which the information is stamped onto the LSB of the image pixel values are unlikely to produce visual artifacts in the image. If an image is altered, the LSB is likely to be changed such that the verification will be able to determine the modification. Such LSB manipulation, however, is not secure against malicious attacks: it is relatively easy to create a system that alters the visual content of an image without changing the LSB of every pixel value, to a degree that the whole image can be modified while the LSB is kept intact. Verification based on the LSB then fails to detect the alterations. Another limitation of some existing techniques is that they cannot determine the exact regions of modification in the verification process; instead, they can only provide a binary answer of whether an image has been modified or not. Such information may be valuable for better security measures. 1. IMAGE VERIFICATlON 2. THE PROPOSED TECHNIQUE As the Internet and the World Wide Web have gained great popularity, it has become commonplace to make collections of images, stored on Internet-attached servers, accessible to vast number of others through the Internet. However, making the images accessible to others through the Internet has also created opportunities for malicious parties to replace images on Internet servers with forgeries, or to intercept and replace images that have been transmitted to others. In addition, with the sophisticated image editing software now available, many have the tools to alter the content of digital images with ease, and with results that mimic the work of the professionals in the traditional photographic medium. To address these concerns, we need to develop techniques that can protect digital images against malicious attacks and intentional alterations. Several invisible watermarking techniques have been reported for data hiding, the embedding of robust watermarks for copyright protection, or the insertion of fragile watermarks for image verification. We shall focus on invisible watermarking techniques for image verification here. Friedman proposed the Trustworthy Digital Camera[ 11 in which a watermarking scheme was incorporated to determine whether a digital photo had been modified using public-key encryption technology. Schyndel et al.[2] discussed coding undetectable digital signatures onto an image through the ma0-8186-8183-7/97 $10.00