Edit in JSFiddle

<!-- Here in the sizes attribute we didn't provide any media query so browser takes the same display width for all screen or viewport sizes. -->
<!-- 50% means that image renders in 50% width of the device width, -->
<img src="http://qnimate.com/wp-content/uploads/2014/06/backup.jpg" srcset="http://qnimate.com/wp-content/uploads/2014/06/retina-2x.jpg 2x, http://qnimate.com/wp-content/uploads/2014/06/normal-1x.jpg 1x, http://qnimate.com/wp-content/uploads/2014/06/512.jpg 512w 1x, http://qnimate.com/wp-content/uploads/2014/06/1024.jpg 1024w" sizes="(min-width: 100px) 100%, (min-width: 200px) 200%, (min-width: 1000px) 300%">