<http://schema.org/thumbnailUrl>
<http://cdn1.tnwcdn.com/wp-content/blogs.dir/1/files/2011/08/Stack-of-Ipads-1vl2mjn-520x245.png>
<http://thenextweb.com/apps/2010/12/04/stack-it-an-incredibly-easy-way-to-manage-and-share-groups-of-links/>