In a comment on my last post
i_kender pointed out that the British Library has put a shedload of illustrations from books on line for free use, as a huge flickr set.
http://www.flickr.com/photos/britishlibrary/ For example, one of the first I found was a larger version of this:
an illustration from
The Angel of the Revolution - I have larger versions on the FF CD-ROM, but there isn't room on my web site.
At the moment the quantity is vast and tagging is minimal, actually finding anything is difficult. But if enough people take an interest it ought to eventually be a very useful resource.