Although the Art History Collection is no longer in Artstor, the collection is an important source of images for the department. Access from a university computer is east. Simply go to http://www.artstor.org/index.shtml and make an account to use it. There are tutorials on the site if needed.
To access from home you must make an account. Then you can use it from home for 120 days. To renew after the 120 days, you must log in again from a computer on campus.