https://www.admonsters.com/blog/pixel-delivery-best-practices
http://www.allaboutcookies.org/web-beacons/
http://stackoverflow.com/questions/20644029/checking-if-a-div-is-visible-within-viewport-using-jquery
https://www.admonsters.com/blog/pixel-delivery-best-practices
http://www.allaboutcookies.org/web-beacons/
http://stackoverflow.com/questions/20644029/checking-if-a-div-is-visible-within-viewport-using-jquery