code: def _pil_props(self):
          
          stream = BytesIO(self._blob)
          pil_image = PIL_Image.open(stream)
          format = pil_image.format
          width_px, height_px = pil_image.size
          dpi = pil_image.info.get('dpi')
          stream.close()
          return (format, (width_px, height_px), dpi)
docs: A tuple containing useful image properties extracted from this image
          using Pillow (Python Imaging Library, or 'PIL').