A great resource has just opened up over at the New York Public Library. They have just digitised over 180,000 of their photos, illustrations, maps and you can download these for free to use as you may as most are no longer under copyright.
“Did you know that more than 180,000 of the items in our Digital Collections are in the public domain?
That means everyone has the freedom to enjoy and reuse these materials in almost limitless ways. The Library now makes it possible to download such items in the highest resolution available directly from the Digital Collections website.

No permission required. No restrictions on use.
Below you’ll find tools, projects, and explorations designed to inspire your own creations—go forth and reuse!”