Usage:

Create a single instance of the WebcamHeadTracker class.
Call WebcamHeadTracker::initWebcam() to initialize the webcam. If this fails, no usable webcam could be found.
Call WebcamHeadTracker::initPoseEstimator() to initialize the head pose estimator. This requires two data files: haarcascade_frontalface_alt.xml from OpenCV and shape_predictor_68_face_landmarks.dat from dlib. If you call this function without arguments, then the library will try to find these files at the places where they were when the library was built. This works fine on development systems and on Linux(ish) systems, but if you deploy your application, you might want to bundle these files.
While WebcamHeadTracker::isReady() returns true:
- Acquire a new webcam frame with WebcamHeadTracker::getNewFrame().
- Compute a new head pose with WebcamHeadTracker::computeHeadPose(). This may fail if no face could be detected in the webcam frame for some reason.
- Get the latest known pose with WebcamHeadTracker::getHeadPosition() and WebcamHeadTracker::getHeadOrientation().