Suppose we have an <img src='http://example.net/image.png' /> that has been loaded and is displayed by the browser. How can we PUT that PNG file to, say, http://example.net/image2.png, preferably without first GETting it again?
My attempt:
fetch('http://www.example.net', {
    method: 'PUT',
    headers: {
      'Content-Type': 'image/png'
    },
    body: // What to put here?
}
