Simple retina <img>

retinaimg.html

<img src="myimage.jpg" data-2x="myimage-2x.jpg">

retinaimg.js

if(window.devicePixelRatio >= 1.2){
    var elems = document.getElementsByTagName('*');
    for(var i=0;i < elems.length;i++){
        var attr = elems[i].getAttribute('data-2x');
        if(attr && elems[i].tagName == 'IMG'){
            elems[i].src = attr;
        } else if(attr){
            elems[i].style.cssText += 'background-image: url('+attr+')';
        }
    }
}