The Smithsonian's photographic Archive (at least parts of it) is available at flickr! The pictures are in high-resolution und published under Flickr commons copyright regulations, i.e. copyright-free.
Most interesting is the Folder 'Portraits of Scientists and Inventors' including many famous scientists from the 19th century (including G. Marconi from the upper left corner...). The pictures are from the Smithsonian Dibner Library of the History of Science and Technology that has a collection of more than a thousand portraits of scientists and inventors through the centuries. Only a small sampling of 144 pictures of the collection is available at flickr and gives you an idea of the range of the collection. Visit “Scientific Identity: Portraits from the Dibner Library” to see the entire collection.
Other interesting folders include 'Portraits of Artists' or 'People and the Post' from the Smithsonian's National Post Museum.
[via boing boing]