Well how do you look when you see a new math problem? Facial recognition software uses a set of measurements (distance between eyes, width of nose, etc.) to create a numerical “faceprint” for a particular image, which can then be compared with a database.
Mood Battle is an experiment to detect emotions by comparing measurements from a face. If you have a webcam, try out some different emotions on it. But if it mistakes your angry face for a happy one, remember: it’s only looking at numbers.