It was just written up in Popular Science:
The Mood Meter came about when a team of researchers at the place from whence all awesome things come, MIT’s Media Lab, hooked up a camera and screen (or projector) to some nifty facial recognition algorithms that can spot faces and smiles in real time. And, after assuring campus security that they wouldn’t be recording any images, they placed the installations in four different locations across MIT’s campus.
Faces deemed to be smiling are augmented on the screen with a big, cartoon smiley face. Frowning and neutral countenances get an emotionless overlay, instead. The software also estimates how big each person’s smile is, on a scale of 0 to 100, and averages the expressions into a happiness barometer rating for the area. It certainly encourages people to try smiling, as you can see in this video.
I walk by this thing every day. It has a strange (but not surprising) psychological effect. If I’m with someone, it usually registers me as a green smiley face. If I’m alone, usually a yellow neutral face. But as soon as I realize I’m not smiling, I immediately force a smile to turn into the green smiley face. I only once got the red frown. I was actually deep in thought, not in a bad mood. But it made me start wondering how serious I look when I’m deep in thought (anyone who’s ever seen me play the guitar would probably answer “very”). And of course I quickly smiled.
Nobody wants to “fail”, and being given a red frown feels a little like getting a check minus on an easy kindergarten (or business school) assignment.