// Random Image Generator Code
	if (document.images) {
	//cache random images	
		img0 = new Image();
		img0.src = "/img/hdr_0.jpg";
		img1 = new Image();
		img1.src = "/img/hdr_1.jpg";
		img2 = new Image();
		img2.src = "/img/hdr_2.jpg";
		img3 = new Image();
		img3.src = "/img/hdr_3.jpg";
		imgDefault = new Image();
		imgDefault.src = "/img/header_img.jpg";
	//if document.images object not supported by browser, do not cache images.
	//instead, assign null values.	
	} else {
		img0 = "";
		img1 = "";
		img2 = "";
		img3 = "";
		imgDefault = "";
	}

	//define function that creates a random number, adds the result to an image souce
	function genImage() {
		var ranNumber = Math.round(Math.random() * 3);
		document.mainImage.src = "/img/hdr_" + ranNumber + ".jpg";
	}
	
window.onload = genImage;