http://www.digitalgallery.emory.edu/luna/servlet (You must LOGIN to get most material)
Metropolitan Museum of Art images [and other IAP(Images for Academic Publishing ) program images] in Artstor http://www.artstor.org/what-is-artstor/w-html/services-publishing.shtml
National Gallery of Art Images, https://images.nga.gov/en/page/openaccess.html
LACMA (Los Angeles County Museum of Art) has 20,000 images avaialble free of copyright restrictions. https://www.lacma.org/image-library