High school history class projects just got a whole lot easier.
Historian Kalev Leetaru has uploaded almost 3 million historical pictures to Flickr.
The pictures have been scanned in to the site's Internet archive page and are in the public domain, so anyone is free to use them.
A lot of these pictures were previously pretty hard to find. You'd have to sort through millions of library books to come up with a collection like this, but now thanks to Leetaru, it is all at our fingertips.
Creating easy access to this many public domain pieces is a huge public service. The World Intellectual Property Organization says, "Many industries require access to copyright material for the purposes of research and development, education, software or hardware interoperability. A lack of reasonable access can actually hurt economic growth."
And The New America Foundation says work from the public domain can lead to the creation of new products, "Though rarely acknowledged, the public domain has always been critical to new creativity."
The BBC says Leetaru began working on this while researching at Georgetown University under a fellowship sponsored by Yahoo, which owns Flickr.
Leetaru made his own software to recognize the pictures and make them searchable online.
The pictures Leetaru added span a wide range of modern history, from 1500 to 1922.