Registering your work with the copyright office is foundational to the business of photography.
A court decision was only possible because the photographer was smart enough to register her work.
If you are already registering your work then good for you!
If you are not registering your work, you should start doing so on a regular basis immediately.
Click the following link to read about the photographer who was awarded over $12million dollars for copyright infringement of seven of her photographs.
http://www.photoattorney.com/2008/06/photographer-gets-12-million-verdict.html