Flickr Commons includes images with “no known copyright restrctions” contributed by more than 100 libraries, archives, and museums.
The Getty Open Content Programmakes freely available nearly 100,000 digital images to which the Getty holds the rights or that are in the public domain.
Google Images has over 10 billion images, but many are low resolution. A subset called Google Art Project features more than 40,000 high-resolution artworks from 46 museums.
Indiana Historical Society has more than 50,000 digital images.
Library of Congress Prints & Photographs Online Catalog has 1.2 million digitized images, as well as records for the 14 million artworks in its collection.
National Gallery of Art's NGA Imagesis a repository of more than 45,000 open access digital images.
New York Public Library Digital Collections includes over 800,000 prints, photographs, maps, and other materials.
VADS (Visual Arts Data Service) has over 100,000 images that are freely available and copyright cleared for use in learning, teaching and research in the UK.
The Victoria and Albert Museumprovides online access to nearly 475,000 images of art and design objects from its collections.
Web Gallery of Art has 35,000 high-resolution images of European visual art created prior to 1900, with special concentrations in Baroque, Gothic, and Renaissance artworks.