These databases will be most helpful for art research.
CAMIO® — OCLC's Catalog of Art Museum Images Online — is a growing online collection documenting works of art from around the world, representing the collections of prominent museums
NGA Images is a repository of digital images of the collections of the National Gallery of Art.
This site is a living database with new materials added every day, featuring prints, photographs, maps, manuscripts, streaming video, and more.
This collection contains 30,000 digital images of paintings, sculpture and architecture, including images from many important collections: the Prado, the Kunsthistorisches Museum, the Uffizi, and the Louvre as well as archeological sites in Greece, Italy, Turkey and Egypt.