eBay would not be able to copyright pictures without the permission of the owners of those pictures. That could be done by inserting a clause in the contract that
eBay sellers must agree to - something to the effect that all pictures become the property of
eBay. But since that could discourage sellers and reduce income to
eBay, I doubt they'd want to make a big deal out of it.
Where was this announcement posted? Was it directly from
eBay?
Another person mentioned that it was becoming more common in photo contests - but actually that's been a common practice for a long time. It's one of the scams by which some magazines acquire photo archives at low cost. They hold photo contests, all submissions become property of the magazine. They pay nominal prizes to a few top winners, and acquire a large
collection of free or low-cost pictures.
eBay certainly doesn't need an archive of low
quality pictures of trivial items, so more likely their advantage would be to try to stop criticism and negative publicity regarding their practices. The resistence they are likely to run into would be from sellers who use their own stock advertising photos, banners and letterheads, etc. Allowing
eBay to acquire ownership and copyright would prevent the sellers from publishing their own catalogues and advertising.