I think the best way to do it is to go to this Art Library's page at http://www.lib.washington.edu/art/
If you're off-campus, click on the off-campus login up in the right hand corner so you can get there through their proxy. Then, about halfway down the page under Art Reference Resources in the blue box, there's a link under Image Collections. I think from there you can make a login of your own so you can save images, and it seems once you've done that it gives you 120 days of access without having to go through the proxy.
I know this is art-geeky but to get to see some of these images up close is so very cool.