It detects whether the person in from of the camera is happy or not .
It uses the Viola Jones Algorithm and coverts live feed image into greyscale. It detects faces and other features using haar like features. Cascading Classifier is used in this project. The cascade is a series of filters that will apply one after the other to detect a face through its features. The required cascading xml files can be found here : https://github.com/opencv/opencv/tree/master/data/haarcascades.
This can be used in cinemas , to detect whether the watcher is happy with the content provided and can serve as a kind of feedback to the content creator.