I read an entry on the New York Times Public Library Blog last week that covered one resource but actually took me to another one. The blog post was about a collection of 1,358 images of Napoleon (or images closely related to Napoleon.) Which was all very interesting but not as interesting as Historical and Public Figures: A General Portrait File to the 1920s, an NYPL archive. It’s available here and contains not only the aforementioned Napoleon portraits but also tens of thousands of public figure images, with most of them focused on the 16th through the 19th-centuries.
If you like you can look at all the portraits at once, but this is a big collection for that. You can also do a search. (There file does have a name index available, but I found it unwieldy; I’d stick to searching.) I did a search for Napoleon, natch, and got 1,755, though many of them were copies and knockoffs of each other. I did another search, this time for Twain, and got 109 results, everything from photos of the man himself, to cartoons, to a sculptor working on a bust of Twain.
Search results have thumbnails, each item also has its own page with some details and the ability to zoom in. (Sometimes you can’t zoom as much as you like — some of the Twain images were dark and there wasn’t sufficient detail.) If you really like an image, you can order a print. If you just want to share it, detail pages also include permalinks and codes for embedding.
Great reference source, especially for kids doing history reports.