<a href="https://drive.google.com/uc?export=view&id=1LuUvsIOntNF8FvlJnvHCLtQGd8yvmDce" class="luminous">
  <img src="https://drive.google.com/uc?export=view&id=1LuUvsIOntNF8FvlJnvHCLtQGd8yvmDce" alt="仲良しな犬">
</a>

img {
  max-width: 250px;
}

new Luminous(document.querySelector(".luminous "), {
  caption: (elem) => {
  return elem.children[0].getAttribute("alt");
  }
});