function image() {
};
image = new image();
number = 0;
// imageArray
image[number++] = "<a href='http://www.rivalboxing.com/en/index.html'><img src='https://www.clicshop.com/stores/rivalboxing/Files/small_banner_home_boxing_canada-e.jpg' border='0' alt=''></a>"

// keep adding items here...
increment = Math.floor(Math.random() * number);
document.write(image[increment]);