There have been times when I've uploaded what I considered to be a "slew" of images to some service, which in reality might have peaked at about 50 or so. But then there's someone like Kalev Leetaru, who comes along and makes 50 seem like an actual drop in a bucket. You see, Kalev has taken on the task of scouring all of Archive.org's public domain book section to extract any and all images that could found. He then pushes them through to a special Flickr account named "Internet Archive Book Images".
As far as I can tell, the job is not finished, but even at this point, a staggering number of extracted images have made their way to this Flickr account - 2.6 million, in fact. See what I mean by my record upload being a "drop in a bucket"?
All of the images found on this Flickr account are public domain, meaning that anyone has the rights to snatch them and use them in any way they see fit. You may wish to pluck some for use in a history project, for example, or even to implement them into a video game. Of course, you can also use them to draw inspiration, and perhaps even study up on things.
A directory of millions of images would be pretty useless without it being searchable, so Kalev has named each and every one in this manner, "Image from page XXXX of '(Book Name)' (Date)", with a real example being, "Image from page 1006 of 'Atlanta City Directory' (1913)". If there's an unfortunate aspect of this collection, there doesn't seem to be a way to search for images exclusively from within it. Instead, any search would be site-wide, though if the name of the book matches anything from the collection, then those images would come up in the search.
That issue aside, this is an extremely cool project, and you could easily lose hours scouring the collection for some extremely interesting, and perhaps even useful, images. There's just one thing I can't help but wonder: How much space does this entire collection take up on Flickr's servers?