You can also seed with unique strings of words. Most readers will read right across them, but you'll know the exact string to search for thus turning up any pirates. Graphics Graphics are really tough. Use the Title as mentioned before. Digital watermarks offer some degree of identify ownership but won't help you search for them.
People really believe that everything on the Web is in the public domain.
It's amazing to find who rips stuff off. I encourage them to go ahead and use the art, but give me a credit, and link back to the Design Center. In many cases, I'm happy to report, they do just that. Court is a drastic measure. First, you'll be called upon to prove that you've lost income due the infringement.