function doThumbHover(ev) {
	var evt = ev ? ev : event; 
	var el = evt.target ? evt.target : evt.srcElement;
	
	while (el.className != "thumbnail" && el.className != "thumbnail_hover") {
		el = el.parentNode;	
	}
	
	el.className = (el.className == "thumbnail") ? "thumbnail_hover" : "thumbnail";
}