Yale University Art Gallery

Website: http://artgallery.yale.edu/collection/search

Conditions:

Thousands of images of works in the Gallery’s collection believed to be in the public domain are available for free download through the Gallery’s website. Under Yale University’s Open Access Policy, anyone may use the Gallery’s open-access material without further application, authorization, or fees due to the Gallery or to Yale.

Source: http://artgallery.yale.edu/using-images

http://ydc2.yale.edu/documentation/faq-open-access-digital-representations-works-public-domain-museum-library-and-archive