The last time (a few months ago) I tried to report an infringing listing I ended up joining eBay's "VeRo" program.

Once I had submitted the paperwork they were pretty fast to act. Here is the info:

http://pages.ebay.com.au/help/policies/programs-vero-ov.html

In the meantime I would encourage you to keep records of things that might prove they are your images

eg take screen shots of the listings (hopefully your item will show an earlier date etc), heck even screen

shots of the image's exif data (which shows when original image was taken and what device was used etc).