Most folks know that the Library of Congress houses an extraordinary collection of photographs that cover the life span of the medium. http://www.loc.gov/rr/print/catalog.html
A good deal of it is pedestrian and much of it is historical but some of it is by the better photographers of the 20th century. What a lot of people don't know is that a good bit of the collection has been scanned and digitized and is available as large, excellent files that are a few clicks away. There are images here by Walker Evans,( the first two above) Lewis Hine, (the third image above) and many others. Sadly the Atget's, donated by Abbot, do not exist as large tiffs. There is a legal page that details the rights and restrictions of these images and goes into some detail of what you can and can not do with these files. While I would never encourage anyone to do anything illegal I do think that, if one was so inclined, one could, with some basic Photoshop skills and a decent Epson printer make quite a few lovely prints from these scans for their personal collection.