An legal copyright is granted to the creator of a work as soon as the work is created. This enables the owner of the material (book, song, photo, etc) to stop someone else from using their work without permission, but until the copyright is officially registered with the Copyright Office, you will not be able sue for past damages.

If all you want to do is put the copyright (or other watermark) symbol on your photo, you have the answer in the first response.