What a very clever idea: Public Domain Illustrations from Old Books
Old Book Illustrations was born of the desire to share illustrations from a modest collection of books, which we set out to scan and publish. With the wealth of resources available online, it became increasingly difficult to resist the temptation to explore other collections and include these images along with our own... We are not the only image collection on the web, neither will we ever be the largest one. We hope however to be a destination of choice for visitors more particularly interested in Victorian and French Romantic illustrations.
Essentially, they have taken illustrations that are out of copyright and made them freely available for anyone seeking artwork for their book. Enjoy - and be sure to follow along on Twitter: @obillustration