If you're not aware of Flickr, or what it is/does/can do, it's an online community for photo sharing...check it out at http://flickr.com. The White House has a photostream, as does the Library of Congress, which is making available to the public via flickr digitized versions of many of the most recognizable images from the Depression-era photdocumentary project conducted by the U.S. Resettlement Organization and the Farm Security Administration, and later the Office of War Information. The project was most active between 1935-1943, and the entire collection was transferred to the Library of Congress in 1944. Perhaps the most iconic and recognizable of all the images is "Migrant Mother" by Dorothea Lange, a landmark photo that put real faces on the plight of regular Americans during the Depression and the Dust Bowl. A set within the LOC's photostream, entitled FSA/OWI Favorites, contains staff picks and other favorite and famous photos from that collection.
It is amazing what's available to the general public via Flickr. It's worth it just to go to the site and see all of the glorious photos taken by people all over the world - but the LOC and White House Pages are a marvel. Some photos are available for download and use for things like research and school projects - however, please keep in mind that copyright restrictions do apply to content posted on Flickr, if you want to use a photo for something more than your own personal edification. At any rate, check it out!