placeholder image
Base64 encoded semi-transparent 1x1px png image.
<img src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mO8Ww8AAj8BXkQ+xPEAAAAASUVORK5CYII=" width="20" height="20" alt="Transparent image"/>
Output:

copy