headers = new Array();
headers[0] = "images/photo_01.jpg";
headers[1] = "images/photo_02.jpg";
headers[2] = "images/photo_03.jpg";
headers[3] = "images/photo_04.jpg";
headers[4] = "images/photo_05.jpg";
var headerMax = headers.length -1;
//
function setHeaderRandom() {
	var randomNr = headerMax * Math.random();
	randomNr = Math.round(randomNr);
	var header_img = headers[randomNr];
	var header_random = "<img src=\"" + header_img + "\" alt=\"De Kennisalliantie foto\" width=\"296\" height=\"215\" />";
	document.getElementById('header_photo').innerHTML = header_random;
}