The Library of Congress has made 3115 photographs from its collections available on Flickr, with no known copyright restrictions. A partial explanation:
We want people to tag, comment and make notes on the images, just like any other Flickr photo, which will benefit not only the community but also the collections themselves. For instance, many photos are missing key caption information such as where the photo was taken and who is pictured. If such information is collected via Flickr members, it can potentially enhance the quality of the bibliographic records for the images.The above photograph is labeled "Unidentified shelf of kitchen utensils and jars of spices [between 1941 and 1945]."
The Library of Congress' photos (Flickr)
My Friend Flickr (Library of Congress blog)