var theImages = new Array()

theImages[0] = 'images/header_image.jpg'
theImages[1] = 'images/header_image2.jpg'
theImages[2] = 'images/header_image3.jpg'
theImages[3] = 'images/header_image4.jpg'
theImages[4] = 'images/header_image5.jpg'
theImages[5] = 'images/header_image6.jpg'
theImages[6] = 'images/header_image7.jpg'
theImages[7] = 'images/header_image8.jpg'
theImages[8] = 'images/header_image9.jpg'
theImages[9] = 'images/header_image10.jpg'
theImages[10] = 'images/header_image11.jpg'
theImages[11] = 'images/header_image12.jpg'
theImages[12] = 'images/header_image13.jpg'
theImages[13] = 'images/header_image14.jpg'

var j = 0
var p = theImages.length;
var preBuffer = new Array()
for (i = 0; i < p; i++){
   preBuffer[i] = new Image()
   preBuffer[i].src = theImages[i]
}
var whichImage = Math.round(Math.random()*(p-1));
function showImage(){
document.write('<img src="'+theImages[whichImage]+'">');
}