The blogger behind Shorpy says, "Most of the photos on this site were extracted from reference images (high-resolution tiffs, 20 to 200 megabytes in size) from the Library of Congress research archive."
In addition to Shorpy's selections from his own and the LC collections, there's also a Member Gallery section where you can upload photos of your own. I uploaded photograph of my grandmother in a Chicago sweatshop, c. 1912. It's one of my prized possessions.
Shorpy is definitely worth checking out.