function image() {
};
image = new image();
number = 0;
// imageArray
image[number++] ="url(images/rotate0.jpg)";
image[number++] ="url(images/rotate1.jpg)";
image[number++] ="url(images/rotate2.jpg)";
image[number++] ="url(images/rotate3.jpg)";
image[number++] ="url(images/rotate4.jpg)";
image[number++] ="url(images/rotate5.jpg)";
image[number++] ="url(images/rotate6.jpg)";
image[number++] ="url(images/rotate7.jpg)";
// keep adding items here...

increment = Math.floor(Math.random() * number);
document.getElementById("top").style.backgroundImage = image[increment];