var theImages = new Array() 

theImages[0] = 'img/left-swap1.jpg'
theImages[1] = 'img/left-swap2.jpg'
theImages[2] = 'img/left-swap3.jpg'
theImages[3] = 'img/left-swap4.jpg'
theImages[4] = 'img/left-swap5.jpg'
theImages[5] = 'img/left-swap6.jpg'
theImages[6] = 'img/left-swap7.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]+'">');
}