docs: def _thumbnail_resize(self, image, thumb_size, crop=None, bg=None):
          """Performs the actual image cropping operation with PIL."""
  
          if crop == 'fit':
              img = ImageOps.fit(image, thumb_size, Image.ANTIALIAS)
          else:
              img = image.copy()
              img.thumbnail(thumb_size, Image.ANTIALIAS)
  
          if bg:
              img = self._bg_square(img, bg)
  
          return img