class_docstr: An abstract class representing a face detector.
  
  Any other face detection implementation must subclass it. All subclasses
  must implement ``detect_from_image``, that return a list of detected
  bounding boxes. Optionally, for speed considerations detect from path is
  recommended.
code: def reference_x_shift(self):
      raise NotImplementedError
  
file_path: face-alignment/face_alignment/detection/core.py
imports: import logging
  import glob
  from tqdm import tqdm
  import numpy
  import torch
  from skimage import io
label_desc: Use image node_id 6 for calling the FaceDetector obj's underlying member method code with example usage: obj.reference_x_shift() without return types