The post processing of my photos are unique and are very easy to spot. (Refer to my below listed website to see) I also digitally embed my personal information on all of my photos that I have on my websites.
There are several websites that can track where all of your photos are located on the web. One site is http://www.tineye.com/. This site does a reverse image search and lists all sites containing your photos.
Proving was very easy as the photos that this person did steal are also being sold at one store that I have licensed to sell my photos and postcards. The same photographs were also on several of my photography websites being sold by me and I am the copyright holder.
In the end, the owner of the store knew that she was caught and did agree to pay me at my rate for stealing eight photographs. At that time, I was selling a 1 meg digital download for $250.00 for a one year license. Larger size files are much more.