Online collections are excellent places to find images of artworks for study or comparative images for other works of art you may be analyzing. Here are several large, useful collections:
Most online images can be used for class papers, class presentations, and even websites under the educational fair use policy, as long as they are only available to your own educational community. "Fair Use" allows scholars, students, teachers, and others to use works that are still in copyright protection for the purpose of education and criticism. This does not mean that any use is fair as long as it is for educational purposes, but education is specifically mentioned as a favored purpose.
Here is a link to Brown University Library's guide for images and copyright:
For more info, here is a link to the MIT Libraries' guide for images and fair use:
Uploading or downloading copyrighted works without the permission of the copyright owner is a violation of TCTC policy and U.S. law.
Legal alternatives to unauthorized downloading link: