https://github.com/ageitgey/face_recognition/blob/c96b010c02f15e8eeb0f71308c641179ac1f19bb/examples/face_recognition_knn.py#L111-L150
https://github.com/ageitgey/face_recognition/blob/c96b010c02f15e8eeb0f71308c641179ac1f19bb/examples/face_recognition_knn.py#L153-L181
