function writeHeaderImage() {
	rnumb = Math.floor(Math.random()*3) + 1;
	document.write("<img src=\"images/header"+rnumb+".jpg\" />");
}

window.onload = function() {
	var petImageHeader = document.getElementById("petImageHeader");
	rnumb = Math.floor(Math.random()*3) + 1;
	petImageHeader.innerHTML = '<img src="/images/header' + rnumb + '.jpg" />';
}