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.
Images of artworks the Met believes to be in the public domain widely and freely available for unrestricted use, and at no cost. Find them by selecting the "Public Domain Artworks" filter in the left-hand column
NASA's website offers access to many of their images, audio files, videos and other media, which are generally not copyrighted and freely available for use.
NGA Images is a repository of digital images of the collections of the National Gallery of Art. On this website you can search, browse, share, and download images.
Images on the Rijksmuseum website are fully searchable and downloadable. Each item that has entered the public domain includes this information in the section of the item description entitled acquisition and rights.
Yale University Art Gallery: "anyone may use the Gallery’s open-access material without further application, authorization, or fees due to the Gallery or to Yale."
