Photographer Carol Highsmith dedicated tens of thousands of images to the public domain a few years ago. There have been questions and controversies about reuse, and specifically, preservation of attribution. Wikipedia Signpost 
But this is an incredible and valuable library of public domain images. We'd like to work with it on Federated Wiki.
Robert Sterbal and Ward Cunningham have been working on this. I need to link to their pages, and I'm not sure I know where they all are.
Highsmith, a distinguished and richly-published American photographer, has donated her work to the Library of Congress since 1992. Starting in 2002, Highsmith provided scans or photographs she shot digitally with new donations to allow rapid online access throughout the world. Her generosity in dedicating the rights to the American people for copyright free access also makes this Archive a very special visual resource. site
__Carol McKinney Highsmith__ (born __Carol Louise McKinney__ on May 18, 1946) is an American photographer, author, and publisher who has photographed in all the states of the United States, as well as the Washington, D.C., and Puerto Rico. She photographs the entire American vista (including landscapes, architecture, urban and rural life, and people in their work environments) in all fifty U.S. states as a record of the early 21st century - wikipedia