code: func (o *httpOps) DownloadImage(u *url.URL) (readSeekCloser, *cacheData, error) {
  	ensureLogger(o.Debug)
  	image, cd, err := o.DownloadImageWithETag(u, "")
  	if err != nil {
  		return nil, nil, err
  	}
  	if cd.UseCached {
  		return nil, nil, fmt.Errorf("asked to use cached image even if not asked for that")
  	}
  	return image, cd, nil
  }
docs: // DownloadImage download the image, duh. It expects to actually
  // receive the file, instead of being asked to use the cached version.