Upon further review, I still do not see where eBay would encourage anyone to use someone elses photo. In fact, at the bottom of this official version from eBay, they address that issue.
http://pages.ebay.com/sell/July2009Update/faq/index.html#advantage\\
"What do I do if someone else submits my photo under their user ID?
You should report any activity that you believe infringes on your intellectual property rights immediately through the VeRO program. You can report the problem here."
The comments I see on the discussion boards about this are just supposition on eBays intent. Nothing is shown to support that. I know there are some who suspect everything eBay does, and some of this is earned by eBay, but in this case, there is nothing sinister about it.
IMHO they will NOT allow or encourage others to use someone elses photo. Just the opposite, since they will give credit and a link to you store in any picture used.