If you toss pictures into the public domain (post them to a newsgroup/website) with no copyright notice do you really have any right to be upset when others use them?

Posting an image on the web does not make it public domain. From ebay's own guidelines:

"Contrary to popular belief, the fact that material is posted on the world wide web does not mean it is in the "public domain" or otherwise free to be taken, copied or used by others. Creators of web content probably have copyright, trademark and other rights in the material they create. Copying, modifying and possibly linking to content created by others could expose you to legal liability.

No Copying Allowed! When you prepare your listings you generally should use only material (text, photographs, etc.) and trademarks/names that you created or own yourself or licensed from the owners.

No Unauthorized Linking to Photos! You cannot link to somebody else's picture (so it appears in your listing) without the owner's permission."

If he does not remove the image, I will begin the process of contacting ebay to have the auction nullified, based solely on ebay's own usage guidelines for its members.