Search here to find Flickr photos that have been licensed under a Creative Commons license. Click on the image license link to learn more about the restrictions for an individual image.
"The Getty makes available, without charge, all available digital images to which the Getty holds the rights or that are in the public domain to be used for any purpose. No permission is required."
A major resource for medical, biomedical, and social history images, both historical and contemporary, Wellcome Images contains over 170 000 images, all available for use under a CC license.
"NYPL Digital Gallery provides free and open access to over 800,000 images digitized from the The New York Public Library's vast collections, including illuminated manuscripts, historical maps, vintage posters, rare prints, photographs and more."
The Smithsonian Freer and Sackler galleries have digitized more than 40,000 images from their collections of Asian art, most of which are available in high-resolution and free of copyright restrictions for noncommercial use.
ArtSTOR is a subscription database, but they do provide free access to some of their collections. Read more about how to search and use their images here.