Thanks to Kalev Leetaru, a Yahoo! Fellow in Residence at Georgetown University, you can now head over to a new collection at Flickr and search through an archive of 2.6 million public domain images, all extracted from books, magazines and newspapers published over a 500 year period. Eventually this archive will grow to 14.6 million images.
Source: New Flickr Archive Makes Available 2.6 Million Images from Books Published Over a 500 Year Period