code: def get_rich_menu_image(self, rich_menu_id, timeout=None):
          
          response = self._get(
              '/v2/bot/richmenu/{rich_menu_id}/content'.format(rich_menu_id=rich_menu_id),
              timeout=timeout
          )
  
          return Content(response)
docs: Call download rich menu image API.
  
          https://developers.line.me/en/docs/messaging-api/reference/#download-rich-menu-image
  
          :param str rich_menu_id: ID of the rich menu with the image to be downloaded
          :param timeout: (optional) How long to wait for the server
              to send data before giving up, as a float,
              or a (connect timeout, read timeout) float tuple.
              Default is self.http_client.timeout
          :type timeout: float | tuple(float, float)
          :rtype: :py:class:`linebot.models.responses.Content`
          :return: Content instance