The databases on this page provide access to millions of images, including paintings, photographs, historical images, graphic art and much, much more. See Get Started with ARTstor for a quick tutorial on using that resource to view, present and manage images. For more detailed information, see the Instructor's Guide to Artstor.
There are a lot of great resources on the web, from museum sites to Wikimedia Commons, where you can find collections of images. Hover your mouse over the links to find out what they contain. Have fun exploring!