The Wellcome Library of the Wellcome Collection in London has made available over 100,000 free images through Wellcome Images. These images are being released under a Creative Commons Attribution (CC BY) license, so you can feel free to use them for any purpose, as long as you credit their source (“Wellcome Library, London”).

Primarily a museum devoted to the history of medicine, the Wellcome Collection’s holdings include artworks by Rowlandson, Gillray, Cruikshank, Goya, Van Gogh, and Muybridge, among others. You can read more about Wellcome Images here.