This New York Public Library digital exhibition consists of over 1,700 images (paintings, engravings, photographs, etc.) depicting ancient civilizations (Egypt, Greece, Rome, etc.) taken from 18th to early 20th century. The collection is massive, and exploring it can be a bit overwhelming at first. The only options to browse through the collection are to display all the images at once (clicking through page after page, organized alphabetically by title) or by viewing parts of the collection grouped by subject headings. But since there are still a lot of different subject headings, this can still take some time. A general 'search' feature is also available, though you can't pick a specific category.
Pretty much all the metadata you could possibly want is provided with each image: creator (if known), format/medium, date produced, the original collection it was taken from, etc. The catalog number in the library is also provided, should you want to go and see that drawing of the kneeling Greek archer you like so much live and in person. Images can be enlarged to a degree, but zooming in is limited to roughly 5x the thumbnail size. A link located on the toolbar near each image lets you purchase a print, should you so desire.
The lack of browsing options would suggest that this is a site for people who know their subject (Classics Majors, I'm looking at you. Well, not at the moment. I'm typing, actually. But... never mind). And, with that in mind, this is a very successful collection. But people without a good background in Classics will have to be content to take their time to figure out the collection, or spend some time wandering around aimlessly (which, honestly, there's something to be said for. There are plenty of interesting things to discover here).