var banner = new Array(4); 
banner[0] = "images/photo/home_02.jpg";
banner[1] = "images/photo/home_03.jpg";
banner[2] = "images/photo/home_04.jpg";
banner[3] = "images/photo/home_01.jpg";

function pickRandom(range, cookieName) {
	currentIndex = readCookie(cookieName);
	
	if(currentIndex == null) {
		currentIndex = 0;
	} else {
		currentIndex++;
		
		if(currentIndex >= range) {
			currentIndex = 0;
		}
	}
	
	createCookie(cookieName, currentIndex);
	
	return currentIndex;
}  

var bannerChoice = pickRandom(banner.length, 'banner');