How to get img id

i have this simple code. But it doesn't work. How create a working code? Please help

<form action="">
<img id="3323" src="http://ift.tt/1CpVkmv"></img>
<input type="button" value="GET ID" onClick="GetID(this.form)">
</form>

<scirpt>
function GetID(f){
img_id = f.img.attr('id');
alert(img_id);
};
</script>