Effective and ineffective digital watermarks

We have entered an era where inexpensive and readily-available equipment can produce perfect copies of digital multimedia materials, such as CD-quality audio, publication-quality images, or digital video. In this environment, it has become easier for malicious parties to make salable copies of copyrighted content without compensation to the content owner. Many media content owners are concerned about the potential loss of revenue from multimedia piracy, especially when the content will be exposed to the Internet. Digital watermarking is seen by many as a potential solution to this problem. Many different watermarking schemes have been proposed. Often, however there is little discussion of how effective a proposed watermarking technique may be at solving a particular problem. We describe a number of proposed image-watermarking application scenarios and form a small number of watermark-application categories. Then, with these applications in mind, we discuss the desired technical properties of watermarks for each category. Finally we discuss some watermarking techniques developed by the authors, in light of the desired properties.