For the study, the Carnegie Mellon team used software from Pittsburg Pattern Recognition, or PittPat. Google bought that company last month. The software can recognize faces in photos and videos.

The researchers did three experiments. First, they collected profile photos from a dating website. Its users try to protect their privacy by not listing their real name. But comparing their photos to pictures on Facebook identified one out of ten people.

In the second experiment, the Carnegie Mellon researchers asked permission to take pictures of students on campus. They compared these to photos on Facebook. This time they correctly identified one-third of the students.

In the third experiment, they tried to see how much they could learn about people just from a photo. They found not only names but birthdates, personal interests and even locations, when people listed them. And Professor Acquisti says the technology is only improving.

ALESSANDRO ACQUISTI: “Because face recognizers keep improving accuracy, because cloud computing keeps offering more power, and because more and more images of ourselves are going to be online, we are getting really close to this future where what we did as a proof of concept will be possible to do by anyone on a massive scale.”

In June, Facebook launched a facial recognition system to help users "tag" or list the names of people in photos. Germany last month became the first country to declare this software an illegal violation of privacy.