function image() {
};

image = new image();
number = 0;

// imageArray
image[number++] = "<img src='images/2.png' border='0' ALT='Häst som äter'>"
image[number++] = "<img src='images/3.png' border='0' ALT='Lejon som latar sig'>"

// keep adding items here...

increment = Math.floor(Math.random() * number);

document.write(image[increment]);