code: func (f *Fetcher) FetchImages(al *apps.Apps) error {
  	return al.Walk(func(app *apps.App) error {
  		d, err := DistFromImageString(app.Image)
  		if err != nil {
  			return err
  		}
  		h, err := f.FetchImage(d, app.Image, app.Asc)
  		if err != nil {
  			return err
  		}
  		app.ImageID = *h
  		return nil
  	})
  }
docs: // FetchImages uses FetchImage to attain a list of image hashes