I came across the digital collection of the Hermitage, and what immediately struck me is the homepage's detail about what technology can be employed to search the collection. In addition to a standard search function that allows a user to search by artist or title, the Hermitage has invested a QBIC tool that allows users to search by color palette or even by creating a sketch! I attempted to try it out on a PC (which is old and slow) but I guess it didn't have the necessary plug-ins or whatever it is that you need, because I couldn't actually perform said QBIC search. However, I feel like this capability opens up a lot of doors for amateur and seasoned scholars and researchers alike because it would in theory allow users to zoom in pretty closely and potentially observe the minutae of an item in the collection. And with a collection like the Hermitage's, which is vast and dates back several centuries, this is huge in terms of conservation and access.
The advance search is pretty great also and goes to a level of specificity that I haven't really seen with other digital collections. For example, you can search by artist's country of origin, theme of the artwork, and even by a specific person depicted in the artwork. It also seems, at least with what I can compare the few other online collections I've interacted with thus far, that there is far less metadata associated with items in the Hermitage's digital collection that with others, or is less consistent (the amount of metadata there is varies from item to item). Most digital archives seem to have more metadata including format, authorship, provenance, and detailed description of the actual item.
It's a pretty amazing collection so I'd recommend taking a look! Enjoy it!
http://www.hermitagemuseum.org/fcgi-bin/db2www/browse.mac/category?selLang=English