Yes, you read that correctly! The New York Public Library has an extensive collection of public domain images, free to download.
“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.”
As I wandered my way through the links my geeky little designer heart danced with joy. I couldn't believe my eyes. The collection includes everything from photographs from the 1700's to old restaurant menus, like the one below from Irving House.
To botanical illustrations, like this gem pictured below, of L, Aloé Common. This site is a living database with new materials added every day, featuring prints, photographs, maps, manuscripts, streaming video, and more.
The collection is a wealth of a resource. With categories like: Ornament and Pattern: Pre-Victorian to Art Deco, Kaleidoscope : ornements abstraits, and Pictures of Science: 700 Years of Scientific and Medical Illustration, you simply can't go wrong.