I'm a believer of protecting your work with registering a copyright of the image with the Library of Congress. It is cheap (only $35 online for a bunch of images) and gives you options should your images be misused that you wouldn't have otherwise. I got turned on to it by reading a book on copyright from the Copyright Zone Blog. Ed Greenberg and Jack Reznicki have been talking about this subject for a while. I would suggest you read their book, but it is out of print currently (ebook coming soon).
The video is a tad over 2 hours, but worth every minute.