function image_swap()	{
	var pos = this.src.lastIndexOf('_');
	var newSrc = this.src.substring(0,pos);
	var img300 = document.getElementById('image_300');
	img300.style.visibility = 'hidden';
	img300.src = newSrc + '_300.jpg';
	img300.onload = function()	{
		img300.style.visibility = 'visible';	
	}
}