From the New York Public Library web site:

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.

Great!

[Via Kottke.org]