function changeHeaderImage(imgId) {
	document.getElementById('mainHeader').style.backgroundImage = "url('"+headerImages[imgId]+"')";
	var nextImageId;
	if(imgId == (headerImages.length - 1))
		nextImageId = 0;
	else
		nextImageId = imgId + 1;
	setTimeout("changeHeaderImage("+nextImageId+")", 10000);
}