Generate random number and place it inside image URL

I want to generate a random number and place it inside an image URL. I found this JS code on the web but it doesn't work:

<script type="text/javascript" language="JavaScript">
number=Math.random()*10000000000000000;
</script>

<img src="http://ift.tt/1QHEvkx"/>

Can someone see whats wrong with the code? Thanks in advance.