<http://schema.org/thumbnailUrl>
<http://www.imore.com/sites/imore.com/files/styles/thumbnail/public/field/image/2013/09/ibooks_ios7_guide_iPhone.jpg?itok=UVYes_Qv>
<http://www.imore.com/ios-7-user-guides-ipad-and-ipod-touch-now-available-ibooks>