The library provides you with two databases that offer access to images of artwork from all over the world.
ARTstor is more comprehensive because it is exclusively focused on compiling images.
Oxford Art Online is primarily focused on providing articles on various artists, works or art, art movements, and art terminology BUT it also includes images of art. While the collection of images is nowhere near as robust as ARTstor it's still worthwhile to check out. Please take the time to explore this database for background on a particular artist, movements, and/or techniques.
If you're looking for Open Access images, including things with Creative Commons licenses or work in the Public Domain, check out the following:
Beyond our databases there are lots of other places you can go to find images of art. Here's just a taste!