Protecting Publicly-Available Images with a Visible Image Watermark

In some cases, it is desired to produce images that are suitable for one application and unsuitable for others. With the Vatican Library Accessible Worldwide and Luther Digital projects, for example, it was desired to make available through the Internet images of Vatican Library and Luther Library manuscripts that are suitable for scholarly study yet are unsuitable as a source for unapproved publication. One of the techniques used to accomplish this is the visible image watermark. Our technical goals for watermarking include (1) applying a readily visible mark to the image that clearly identifies its ownership, (2) permitting all image detail to be visible through the watermark, and (3) making the watermark difficult to remove. In this paper, we will describe the technique we use. We will also discuss the characteristics of good watermarks and options we have used in their application. Illustrative watermarked images will be presented.