Does anyone in the reader/viewership of this blog have experience using ARTstor? Our library subscribes to it. It looks awesome, though I haven't yet noodled around enough to determine precisely how it's awesome. There's a clip on YouTube that explains some of the basic features. In addition to searching images you can sort by title, creator, or date, create collections for students to view online, and download gorgeous high-res images for use offline (conference presentations, anyone?). You can also move all around in the image space itself, and zoom in quite close to observe details in images. Obviously art historians of all kinds must find this incredibly useful, but I'm interested especially in the access to photography and American Studies collections this database affords.
The above image is a screen grab from a keyword search on "Abraham Lincoln." And here's Lincoln's hand; I zoomed in on the earliest authenticated photograph of him, believed to date from 1846-47.
I'm lovin' it so far.