http://www.artstor.org/info/index.html
(ARTstor is a digital image database containing more than 300,000
art images and descriptive information for noncommercial and
scholarly, non-profit educational use.)
http://ica.princeton.edu/
(Founded in 1917, the Index of Christian Art is a resource based
at Princeton University)
http://www.netserf.org
(Self-proclaimed as “the internet connection for medieval
resources,” NetSERF is an annotated directory of Web sites
on medieval topics.)