Creative works published before 1923 are legally part of the public domain. Beyond that, the federal government can't copyright anything, except in very specific circumstances.
So why is the Smithsonian Institution claiming copyright on a collection of 19th-century seed catalog images?
What Would Luther Burbank Do? is a project aimed at convincing the Smithsonian to change its policy and make American cultural history available to Americans, a move that would put its policies in line with those of the National Archives, the Library of Congress, and the Government Printing Office.
Public.Resource.Org is going to file a complaint about this and is collecting statements from any member of the public who'd like join. If you have some thoughts about why you think the Smithsonian should let these images be part of the public domain—or if you'd just like to have your name added to the formal complaint—please send a postcard to:
What Would Luther Burbank Do?
1005 Gravenstein Highway North
Sebastopol, CA 95472