These open-source databases can be used for finding high-resolution images of art and objects, as well as photographs, manuscripts, and more. Many are provided by museums and other cultural institutions and are freely available to the public.
Archives of American Art - Part of the Smithsonian Institution; this is a collection of primary sources relating to over 200 years of American art history, including letters and diaries, manuscripts, photographs, and more.
Digital Scriptorium - A consortium of American libraries and museums providing free access to medieval and Renaissance manuscripts.
Digital Public Library of America - A repository of images, text, video and more from across the United States. This collection is freely available to the public.
Europeana Collections - Europeana provides access to millions of books, paintings, films, museum objects and archival records that have been digitized by European cultural and scientific institutions.
Google Arts & Culture - Google provides high-resolution images of art and objects from museums and cultural institutions around the world.
Visual Arts Data Service (VADS) - A portfolio of visual art collections from the U.K. comprising over 100,000 images that are freely available and copyright cleared for use in learning, teaching and research.