Historypin is a crowdsourced project to document the history of the world through photographs, sound and stories. Users can upload photographs to add to the collection. Images are then 'pinned' onto a map. Images can be found geographically, but also temporally. Want to see your town now? And how it looked in 1870? Use the map, and then the timeline slider to narrow things down.

You can also superimpose photographs on Google's street view for comparison.

The site was created by We Are What We Do, in partnership with Google.

There is a good introduction on YouTube. According to the site, 72,042 photos, videos, audio clips and stories have been uploaded and pinned so far.