The Anvil Facetracker is a plugin that automatically creates annotations for head movements. It has two modi operandi:
1. Create annotations when the head's velocity is above some preset threshold 2. Create annotations when the head's acceleration is above some preset threshold.
The acceleration of the head is a direct consequence of forces being exerted on the head, which can be gravity, but more commonly are the due to the muscles in the body, especially in the neck.
The software is based on face recognition algorithms implemented in OpenCV (http://sourceforge.net/projects/opencvlibrary/). The bridge between the C- world of OpenCV and the Java world of Anvil is created by JavaCV (http://code.google.com/p/javacv/).