Have you used ARTstor?
The ARTstor Digital Library
is a nonprofit resource that provides more than one million digital images in the arts, architecture, humanities, and sciences with an accessible suite of software tools for teaching and research. Their community-built collections comprise contributions from outstanding international museums, photographers, libraries, scholars, photo archives, and artists and artists' estates.
ARTstor Digital Library promotes and shares collections from hundreds of museums, artists, artists' estates, photographers, scholars, special collections, and photo archives. Their collections serve the interdisciplinary teaching and research needs of scholars, curators, educators, librarians, and students.