Flickr now has over 1 million images from the public domain courtesy of the US Library of Congress, asking users to help tagging:

http://www.flickr.com/commons

"No known copyright restrictions" is not quite the same as "public domain", although it may be near enough for some purposes.

But these are in the public domain as far as I know. For instance, one set is from 1910 (pre-1923) which I think puts them in the public domain, and another set is from US government sources, which I think puts them in the public domain.... e.g. Wikipedia says, "Works created by an agency of the United States government are public domain at the moment of creation."

I think they should offer an easy zip file of the sets though – it looks like a good image data set to have some fun with for data mining purposes or the like.

kewl I just added the feed to my google screensaver!!

The figure of a million photos relates to the LOC collection – it's not how many have been placed on Flickr.

There are two collections available via Flickr, totaling just over 3000 photos.

Ah, OK. I had the information from Drawn.ca:

<<What do you do with a million public domain images that need context and description?

The Library of Congress is putting them on Flickr.>>