var img_off = new Image();  img_off.src = 'images/center_banner_off.png';
var img_on = new Image();   img_on.src  = 'images/center_banner_on.png';

function blink() {
	var e = document.getElementById("blinker");
		e.src = (e.src == img_on.src) ? img_off.src : img_on.src;
		setTimeout("blink();", 500);
	}