It was fortunate, then, to run across a link at Boing Boing which led me to a fascinating photo collection at Flickr Commons, to which the New York Public Library has just begun contributing, of images that have no known copyright restrictions.
As the NYPL states:
Starting this past January with The Library of Congress, and continuing with places such as The Smithsonian Institution, The Brooklyn Museum, The National Maritime Museum, The National Library of New Zealand, the Nationaal Archief of the Netherlands and numerous others, the Commons has grown steadily over the past year into a truly remarkable public photography resource.
Remarkable indeed. A quick browse through the archive brought up some interesting snaps. (Click for full-size images.)
Midsummer day, Bronx Park, 1911 (Library of Congress)
Blanche Rogers, with pistol. (Library of Congress)
Jiu-Jitsu for Women (George Eastman House collection)