code: func (r *Session) LookupRemoteImage(imgID, registry string) error {
  	res, err := r.client.Get(registry + "images/" + imgID + "/json")
  	if err != nil {
  		return err
  	}
  	res.Body.Close()
  	if res.StatusCode != 200 {
  		return newJSONError(fmt.Sprintf("HTTP code %d", res.StatusCode), res)
  	}
  	return nil
  }
docs: // LookupRemoteImage checks if an image exists in the registry