Responsive Images w/ Modernizr. Source: http://craftedpixelz.co.uk/blog/conditional-js-with-modernizr-mq/

gistfile1.html

<img class="img" src="http://placekitten.com/320/480" alt="" data-big="http://placekitten.com/1024/768" />

gistfile2.js

$(".img").each(function() {
  if (Modernizr.mq('only screen and (min-width: 600px)')) {
    $(this).attr("src", $(this).attr("data-big"));
  }
});