<img src="img.jpg?rand=<?=rand(1,1000);?>" />

<script language="javascript">
document.write('<img src="img.jpg' + Math.ceil(Math.random() * 10000) + '" />');
</script>

<script type="text/javascript">
	function refreshImage(imageId) {
		var objImage = document.getElementById(imageId);
		var oldSrc = objImage.src;
		var cleanSrc = oldSrc.substr(0, oldSrc.indexOf('?'));
		var newSrc = cleanSrc + "?" + Math.ceil(Math.random() * 10000);
		//alert(newSrc);
		objImage.src = newSrc;
	}
</script>


<!-- Put at least one ? here -->
<img src="yours.jpg?" id="your-image" />

<input type="button" value="refresh" onclick="refreshImage('your-image')" />