You can search ARTstor by the name of an art work, by geography, by classification (for example, architecture), or by collection (for example, Beyond the Taj). Use the Advanced Search to limit by date.
Helpful videos on using ARTstor can be found on UTube
National Galley of Art | NGA Images a repository of digital images of the collections of the National Gallery of Art
OAIster: union catalog of digital resources
MADID (Yale University Manuscripts & Archives Digital Images Database)
VIA (Harvard University Visual Information Access)
Bridgeman Art Library: art, culture & history images