The Archives of American Art at the Smithsonian Institution has donated nearly 300 Works Progress Administration (WPA) photographs from the 1930s to Wikimedia Commons, the image collection affiliated with Wikipedia. These include portraits of artists like Charles Alston and Arshile Gorky, and photos showing artists at work on public murals and other Great Depression-era projects. You can view the complete collection here.
As works created explicitly for the Federal Government, most WPA works are not copyrightable and have therefore always been in the public domain. That means you can legally download and use these high-resolution images however you want, without having to seek permission.
Read more about this Smithsonian-Wikimedia collaboration here.