code: def set_rich_menu_image(self, rich_menu_id, content_type, content, timeout=None):
          
          self._post(
              '/v2/bot/richmenu/{rich_menu_id}/content'.format(rich_menu_id=rich_menu_id),
              data=content,
              headers={'Content-Type': content_type},
              timeout=timeout
          )
docs: Call upload rich menu image API.
  
          https://developers.line.me/en/docs/messaging-api/reference/#upload-rich-menu-image
  
          Uploads and attaches an image to a rich menu.
  
          :param str rich_menu_id: IDs of the richmenu
          :param str content_type: image/jpeg or image/png
          :param content: image content as bytes, or file-like object
          :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)