This issue has been discussed for a while now. First
on English Wikipedia, now on Commons.
The discussion on Commons can be found at:
http://commons.wikimedia.org/wiki/Template:Deletion_requests#Official_paint…
A lengthy debate on English Wikipedia is at:
http://en.wikipedia.org/wiki/Wikipedia:Possibly_unfree_images/US_government…
The debate in short: The paintings are not Work of the
United States Government, they were made by artists on
commission. Can they be used as public domain?
/ Fred