Use this guide to help you find images for your art history, studio art, and design courses. (Originally written by Heather Lowe of the Visual Resource Center.)
The VRCs Image Library is a digital image resource that supports teaching and research in art and art history, and a variety of related disciplines at both the undergraduate and graduate level
Wikimedia Commons is a "good faith" free image repository, with items contributed by volunteers. Most images may be reused (see the license details for each) but the quality and resolution varies wildly.