You're thinking of the Copyright Office, not the Patent Office -- patents are for inventions, copyrights are for created works (literature, art, etc.)
However, a bit of gentler advice: the first thing you should always do is contact the site directly. Send them a nice but firm email stating that they are using your photos, and then some sort of conditions -- for example, they can continue using them only if they give you credit and a link, or they can use them only by paying a fee, or they must take them down immediately.
Many sites will be quite happy to comply. Chances are that they didn't know what they were doing -- found your images through an image search, or from somewhere else using your photos without permission.
It's always worth trying to be nice first. You may get a customer out of the deal.