What is it? We live in a digital age where images and videos are captured all the time. These images have information about real places in the world. Even the picture you took of your kids playing in the backyard contains information about that space! These images are often posted to someone's blog, a photo sharing site, a family picture album website or even on postcards in your local gift shop. Imagine taking all of those pictures and mining the relationships between them to create a model of that space in three dimensions.
Official site also found here.