In some of my poking around on-line looking for pictures of something-or-other fantasy-related, I came across this web site put together by the Cornell Institute for Digital Collections. Check it out.
There's some interesting stuff here, and I've used it as a resource a couple of times. It doesn't have good samples of most of my favorite fantasy creatures, I'm sorry to say, and I happen not to be particularly interested in stuff illustrating satanism and insanity, but I really like the Fantastic Space category, as well as what the Bestiary does have. The images all come from Cornell's rare books and manuscripts, so it makes no claim to be historically comprehensive or anything like that. What it does do is make available for viewing sources that otherwise would be hidden away in the archives where we'd never get to see them. I'm always in favor of that!
In addition to the pictures, there are short essays introducing the various categories in the collection: Angels & Demons, the Marvelous, the Grotesque, etc. Under "About this Site" there's an explanation of what sorts of stuff were chosen and how the site was envisioned, with some definition of "fantastic."
At any rate, it seemed as if impending Hallowe'en was a good season in which to draw attention to this collection of strange, spooky, magical, and mysterious images.
(As for these sample images I've chosen, notice how the wood engraving at the top has a different look from the metal engraving in the middle. Remember that wood engravings are relief prints while metal engravings are intaglio... And then there's this strange squid-bishop thing, which is just silly.)
[Pictures: Letter G with triple-headed dragon, wood engraving from La Vie Execrable de Guillemette Babin, Sorciere by Maurice Garçon, 1926;
Labyrinthine dungeon, metal engraving by Piranesi, 1750;
Merman reminiscent of the clergy, wood block print from Icones Animalium, 1560.]