You can serve a DMCA notice to the site(s) using your photos. If no response go directly to their host and you will get an immediate response because if they don't take action they can be held responsible.
As far as protecting them you can slow people down but you'll never be able to stop someone such as me from copying them no matter what you do. If it can be seen I can make copy of it if not directly getting the file then there is certainly many other tools available. Most of the methods involve tricks used in HTML, for example you can set the image as a background image in an HTML element such as a table cell then place a transparent .gif over the top of it. When they right click and save the image they are saving the transparent .gif
Simple trick but quite effective to stop those that don't know any better.
Other things you can do is use the EXIF/IPTC meta data in images. You can use tools like Irfanview or Exifer to insert your copyright. They both have batch modes so you can do a mulititude of images with a few clicks. One thing to note is this information can be changed or even deleted by someone else. Matter fact the "Save for web" option in most imaging applications deletes this by default to save a few bytes. Some software doesn't preserve it and even server software that my resize or manipulate images may discard it. I'm not aware of any search engines that index this information but I'm sure at some point you can expect Google to use it so it might be prudent to take advantage of it.
Lastly you can watermark the image and there are two methods to doing this. A visible watermark is the most common, I'd suggest using a transparent one with a textured gradient color fill as these are the hardest to remove manually. The other method is an invisible watermark, there are services for this and plug-ins available. Digimarc is one comapany that offers this. The transprent watermark can't be seen but can be detected by softwre looking for it.
The one issue with transparent watermarks is they are mebedded in the image data itself and if the image is resampled it can be destroyed in the process. I'm not aware of any free options for applying these but I'm sure they exist.