Locations of online photos may reveal your friendships, says a research by Cornell University computer scientists. When two people posted photos several times from the same locations and at the same time, this was a good predictor that those people were socially connected.

It's not that you know with certainty, but it's a high likelihood that these people know each other, said Dan Huttenlocher, dean of the Faculty of Computing and Information Science, who co-conducted the study.

The researchers found the probability increases as the analysis moves to smaller areas and shorter time spans.

The researchers used a database of some 38 million photos uploaded to the Flickr photo-sharing website by about a half million people. The time and place where photos were taken was provided by GPS-equipped cameras or by people who used Flickr's online-interface to indicate the location on a map.

The same conclusions might be drawn from credit card purchases, fare card transactions on the bus and subway, and cell phone records, they suggested.

While it's obvious that a photo you post online reveals information about what is pictured in the photo, what is less obvious is that as you post multiple photos you are probably revealing information which may not be pictured anywhere, Huttenlocher said.