code: func localImageMagick() string {
  	bin, err := exec.LookPath("magick")
  	if err != nil {
  		return ""
  	}
  	magickHasHEIC.Lock()
  	defer magickHasHEIC.Unlock()
  	if magickHasHEIC.checked {
  		if magickHasHEIC.heic {
  			return bin
  		}
  		return ""
  	}
  	magickHasHEIC.checked = true
  	out, err := exec.Command(bin, "-version").CombinedOutput()
  	if err != nil {
  		log.Printf("internal/images: error checking local machine's imagemagick version: %v, %s", err, out)
  		return ""
  	}
  	if strings.Contains(string(out), " heic") {
  		magickHasHEIC.heic = true
  		return bin
  	}
  	return ""
  }
docs: // localImageMagick returns the path to the local ImageMagick "magick" binary,
  // if it's new enough. Otherwise it returns the empty string.