class_docstr: Randomly crop images and make sure to contain at least one intact
  instance.
code: def crop_img(self, img, bbox):
      assert img.ndim == 3
      h, w, _ = img.shape
      assert 0 <= bbox[1] < bbox[3] <= h
      assert 0 <= bbox[0] < bbox[2] <= w
      return img[bbox[1] : bbox[3], bbox[0] : bbox[2]]
  
imports: import numpy
  from PIL import Image, ImageDraw
  import cv2
  from shapely.geometry import Polygon
  import math
  from ppocr.utils.poly_nms import poly_intersection
label_desc: Use image node_id 4 for calling the RandomCropPolyInstances obj's underlying member method code with example usage: obj.crop_img(img, bbox) and returns: img