code: func imageWithTagString(image string) string {
  	namedRef, err := reference.ParseNormalizedNamed(image)
  	if err == nil {
  		return reference.FamiliarString(reference.TagNameOnly(namedRef))
  	}
  	return ""
  }
docs: // imageWithTagString takes an image string, and returns a tagged image
  // string, adding a 'latest' tag if one was not provided. It returns an
  // empty string if a canonical reference was provided