img = new Array(5);
img[0] = new Image()
img[0].src='images/Image1.png';
img[1] = new Image()
img[1].src='images/Image2.png';
img[2] = new Image()
img[2].src='images/Image3.png';
img[3] = new Image()
img[3].src='images/Image4.png';
img[4] = new Image()
img[4].src='images/Image5.png';

cont = 0;

function trocaimagem() {
	obj = document.getElementById('header_image');
	obj.src = img[cont].src;
    window.setTimeout("trocaimagem()", 10000);
    cont = (cont+1)%5;
}