title: Given dlib's 68-point facial landmarks, determine how good they are
body: <p>I'm using dlib to do face detection, followed by 68-point facial landmark detection. Generally this works very well.</p>
  
  <p>However, dlib's face detector sometimes detects faces where (for example) only one eye is visible, or the person's mouth is not visible (or in rare cases, non-faces). Obviously in these cases some of the 68-points detected are garbage.</p>
  
  <p>How can I detect these cases?</p>