Digital Watermarking

Abstract

Abstract The advent of the Internet has resulted in many new opportunities for creating and delivering content in digital form. Applications include electronic advertising, real‐time video and audio delivery, digital repositories and libraries, and Web publishing. An important issue that arises in these applications is protection of the rights of content owners. It has been recognized for quite some time that current copyright laws are inadequate for dealing with digital data. This has led to an interest in developing new copy deterrence and protective mechanisms. One approach that has been attracting increasing interest is based on digital watermarking techniques. Digital watermarking is the process of embedding information into digital multimedia content such that the information (which is called the watermark) can later be extracted or detected for a variety of purposes, including copy prevention and control. Digital watermarking has become an active and important area of research, and development and commercialization of watermarking techniques is deemed essential to help address some of the challenges faced by the rapid proliferation of digital content. In the rest of this article, it is assumed that the content being watermarked is a still image, though most digital watermarking techniques are, in principle, equally applicable to audio and video data. A digital watermark can be visible or invisible . A visible watermark typically consists of a conspicuously visible message or a company logo indicating the ownership of the image. On the other hand, an invisibly watermarked image appears very similar to the original. The existence of an invisible watermark can be determined only by using an appropriate watermark extraction or detection algorithm. In this article, we restrict our attention to invisible watermarks. An invisible watermarking technique generally consists of an encoding process and a decoding process. Invisible watermarking schemes can also be classified as either robust or fragile . Robust watermarks are often used to prove ownership claims and so are generally designed to withstand common image processing tasks such as compression, cropping, scaling, filtering, contrast enhancement, and printing/scanning, in addition to malicious attacks aimed at removing or forging the watermark.