I'm using Netscape on a Mac, but try this (assuming the operations are the same on a PC):
First, load the eBay page that contains the image you want to save.

On the menu bar, pull down View and click on Page Info. Scroll through the list of objects & pages until you find the address of the image you want. Highlight it, then copy & paste the address into your browser & click. It should show only the image.

Now, just go to File on the menu bar, pull down and click on "Save As", and name & save it where you want to.