With this background ... consider downloading the appropriate image size according to how it would be displayed on the page, as dictated by your CSS rules, rather than assuming it takes up ...

Mobile-oriented, fast and extensible jQuery plugin for lazy loading of images/videos. Currently tested in IE 6-11, Chrome 1-47, Firefox 1.5-43.0, Safari 3-9, Opera 10.6-34.0, iOS 5-9, Android 2.3-5.1, ...