The databases on this page provide access to millions of images, including paintings, photographs, historical images, graphic art and much, much more. See Getting Started with ARTstor for help with setting up an account, accessing the digital library, and more. For more detailed information, see the Instructor's Guide to Artstor.
"Wikimedia Commons is a media file repository making available public domain and freely-licensed educational media content (images, sound and video clips) to everyone..Unlike traditional media repositories, Wikimedia Commons is free. Everyone is allowed to copy, use and modify any files here freely as long as they follow the terms specified by the author; this often means crediting the source and author(s) appropriately and releasing copies/improvements under the same freedom to others."
There are a lot of great resources on the web, from museum sites to Wikimedia Commons, where you can find collections of images. Have fun exploring!