Marco Chiesa:
the Law assigns a sort of copyright to the museum, even if the work of art is photographed by a random visitor.
And even against the panorama freedom...
Regarding the NPG images, I think the main problem would be that a UK reuser would infringe the NPG copyright, while she reads that those images are PD; the NPG may decide that suing Wikipedia is not a great idea, but suing some British student that puts up his own website may be; transiting through the US to remove copyright appears to me as a kind of money laundering...
In fact somebody said that we should add «A template "don't use in... because..."»[1].
Nemo
[1] http://commons.wikimedia.org/w/index.php?title=Commons:Deletion_requests/Nat...