I ran across an interesting service called TinEye that claims to be able to find images on the Internet that are similar to one that you supply. I have been asked many times about tools to search the Internet for unauthorized listing photos, so I decided to give it a try.
Being a “staffer”, I don’t have any listings, so I decided to try it out on the logo for REALTOR.org. Just to “push” the envelope, I used a PNG rendering of the logo.
To my surprise it worked! I received a page full of search results that I could click on to see the image in context. In my case, the logo was found on several International association sites. The result set also contained similar logos. At NAR, all of our groups use a similar “swoop” in the logo, including REALTOR.com.
You must set up an account with TinEye before you use the service. Please read the terms and conditions of service. The site is in BETA right now and has both a Flash and non-Flash interface.
Your mileage may vary, but I would be interested if TinEye can find all of the places you expect your property photos to be.