I had that problem a few years ago. Someone copied one of my listing. Tried to contact him but he would not delete his listing.
By chance, at that time I was using a lot of picture (I was selling clothing) so I was hosting them on a free photo hosting service. I changed one of the picture to this without chaging the file name:
This image was given to me by another seller on eBay.com and he (or she) gave permission to use it to everyone..
The best thing is that since browsers cache pictures (local copy to save download time), the seller did not see that image but he was still seeing the original one. The customers, going for the first time to the auction were seeing the rat... It took him about 3 days to delete the content of his auction!!!