<http://schema.org/image>
<http://rack.3.mshcdn.com/media/ZgkyMDEyLzEyLzA0LzkyL2hvd3RvY3JlYXRlLmJXVy5qcGcKcAl0aHVtYgkxMjAweDYyNyMKZQlqcGc/a8393cc2/ab4/how-to-create-an-engagement-index-42e18b744d.jpg>
<http://mashable.com/2011/12/19/create-engagement-index/>