History Pin: Overlaying Google Street View with Historical Photos

"History Pin hopes to become the largest user-generated archive of the world's historical images and stories. The website acts like a digital time machine, and uses Google Maps and Street View technology to allow the wide public to dig out, upload and pin their own old photos, as well as the stories behind them, onto an interactive map. Uniquely, Historypin lets people layer old images onto modern Street View scenes, providing a series of geo-located time tunnel views into the past."

http://infosthetics.com/archives/2010/06/history_pin.html