Researchers and designers often require a broad range of historical visual images. Below are some resources that serve as good starting places, though many of them are more focused on fine arts (rather than film stills and documentation).
Formerly Grove Art Online, it includes the entire 34 volumes of The Dictionary of Art, with articles as well as links to images on gallery and museum web pages around the world. Includes biographies of artists and searchable images.
Calisphere is your gateway to digital collections from California's great libraries, archives, and museums. Discover over 2,125,000 images, texts, and recordings.