function randomHeader() {
	var imgName = new Array("hd-image1.jpg", "hd-image2.jpg", "hd-image3.jpg", "hd-image4.jpg");
	var rndNum = Math.floor(Math.random() * imgName.length);		
	document.getElementById("header-image").src = "content/images/" + imgName[rndNum];	
}

randomHeader();