ну дык и сделайте как у них, подключите три скрипта и реализуйте сохранение как в демо:
<!DOCTYPE html>
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8" />
<style type="text/css">
div {
width:200px;
background-color: green;
}
</style>
<script type="text/javascript" src="http://eligrey.com/demos/FileSaver.js/Blob.js"></script>
<script type="text/javascript" src="http://eligrey.com/demos/FileSaver.js/canvas-toBlob.js"></script>
<script type="text/javascript" src="http://eligrey.com/demos/FileSaver.js/FileSaver.js"></script>
<script type="text/javascript" src="http://night-creature.com/html2canvas.js"></script>
<script src="http://code.jquery.com/jquery-1.9.1.min.js"></script>
</head>
<body>
<div id="downimg">
<div>
some text
</div>
</div>
<script language="javascript">
function downimg(){
html2canvas($('#downimg'), {
proxy: 'http://html2canvas.appspot.com/query',
onrendered: function (canvas) {
canvas.toBlob(function(blob) {
saveAs(blob, "ololo.png");
}, "image/png");
}
});
}
</script>
<a href="javascript:void(0)" onClick="downimg()" >SAVE</a>
</body>
</html>