<!DOCTYPE html>
<head>
<title>Example</title>
</head>
<body>
<!-- An image should be annotated. -->
<div>
<img src="red.png" width=16 height=16>
</div>
<!-- An image in an anonymous iframe should be annotated. -->
<iframe></iframe>
<script>
let iframe = document.querySelector('iframe');
iframe.contentDocument.body.innerHTML = `
<img src="green.png" width=16 height=16>
`;
</script>
</body>