var theImages = new Array()

theImages[0] = '/images/castings1.jpg'
theImages[1] = '/images/castings2.jpg'
theImages[2] = '/images/castings3.jpg'

var j = 0
var p = theImages.length;
var preBuffer = new Array()
for (i = 0; i < p; i++){
   preBuffer[i] = new Image()
   preBuffer[i].src = theImages[i]
}
var whichImage = Math.round(Math.random()*(p-1));

function showImage() {
	var chosenImage = document.getElementById("focus-box");
	chosenImage.style.backgroundImage = "url("+theImages[whichImage]+")";	
}