"ARTstor is a non-profit initiative, founded by The Andrew W. Mellon Foundation, with a mission to use digital technology to enhance scholarship, teaching, and learning in the arts and associated fields. "
ARTstor is a subscription service, which means the UW pays an annual fee to use the digital library. I hope you will try using ARTstor to see if the images they have can be of use to you!
There are several training videos about ARTstor on YouTube:
If you want to see other ARTstor videos, go to YouTube at
http://www.youtube.com/
and search for ARTstor.
ARTstor has extensive coverage of the cave paintings at Dunhuang, for example,

and a number of really fine Cezannes.

Alan Michelson, the architecture librarian, and I are always ready to help users with ARTstor; drop by the BCE Library or the Visual Resources Collection for assistance!
Heather
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Heather Seneff
Visual Resources Collection
College of Built Environments
University of Washington
http://www.caup.washington.edu/vrc/
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