def get_face_area(face):
    """
    Computes the area of the bounding box ROI of the face detected by the dlib face detector
    It's used to sort the detected faces by the box area

    :param face: dlib bounding box of a detected face in faces
    :return: area of the face bounding box
    """
    return (face.left() - face.right()) * (face.bottom() - face.top())