Digimarc

You already have this one. It comes with Photoshop, but you might not know what it does. It's not exactly a filter because it doesn't change your picture. Instead, it protects your work by placing a digital watermark on it, and a copyright symbol in the title bar. When you register with Digimarc, they'll send you an ID that will let you embed the digital copyright information into the file. When someone views a Digimarc watermarked file in Photoshop, they'll see a dialog box like the one in Figure 19.13, directing them to the website for more information. No one should use your work without your permission.

Figure 19.13. Prevent theft of copyrighted materials.