function image() 
{
};

image = new image();
number = 0;

// imageArray
image[number++] = "<img src='/images/head1.jpg' border='0'>"
image[number++] = "<img src='/images/head2.jpg' border='0'>"
image[number++] = "<img src='/images/head3.jpg' border='0'>"
image[number++] = "<img src='/images/head4.jpg' border='0'>"
image[number++] = "<img src='/images/head5.jpg' border='0'>"
image[number++] = "<img src='/images/head6.jpg' border='0'>"
image[number++] = "<img src='/images/head7.jpg' border='0'>"
image[number++] = "<img src='/images/head8.jpg' border='0'>"
image[number++] = "<img src='/images/head9.jpg' border='0'>"
image[number++] = "<img src='/images/head10.jpg' border='0'>"
image[number++] = "<img src='/images/head11.jpg' border='0'>"
image[number++] = "<img src='/images/head12.jpg' border='0'>"

// keep adding items here...

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

document.write(image[increment]);