I wonder what the copyright situation is with these photos of public domain works. I seem to recall that Wikipedia extracted the images from a similar system used by the National Portrait Gallery in the UK and a legal spat ensued.
Crucially, UK copyright law gives you rights in some stuff just because you put effort into it ("sweat of the brow") while US law has a precedent requiring creativity, so a photo of a statue is copyrighted to the photographer, but photograhps of flat objects don't.
It looks like the NPG asserts that use of the images is illegal, but isn't willing to sue the Wikimedia Foundation over it, so they're at something of a stalemate with Wikimedia de-facto winning (but with no guarantees for other parties who aren't Wikimedia). Wikimedia's official position seems to be more or less an ultimatum of, "these are public domain, sue us if you think we're wrong": http://commons.wikimedia.org/wiki/Commons:When_to_use_the_PD...
Crucially, UK copyright law gives you rights in some stuff just because you put effort into it ("sweat of the brow") while US law has a precedent requiring creativity, so a photo of a statue is copyrighted to the photographer, but photograhps of flat objects don't.