Actually //moodle.blackpool.ac.uk/ uses a slightly simpler script than that found on javascript.internet.com. Here is their script:
<script type="text/javascript">
<!--
var images = new Array();
images[images.length] = new Array('', 'image1.jpg');
images[images.length] = new Array('', 'image2.jpg');
var randomNum = Math.floor(Math.random() * images.length);
document.write("<div style='width: 100%; height: 390px; background-image: url(/file.php/1/home_images/" + images[randomNum][1] + "); background-repeat: no-repeat; background-position: center center;'></div>");
//-->
</script>
Suppose you want to add this script to your front page:
1. Edit the topic section
2. Toggle html (click the <> icon in the toolbar)
3. Paste the above script into the editor
4. For each image you want to display add an image line to the list in the script
images[images.length] = new Array('', 'image2.jpg');
Change the image name in the line to the name of your image.
5. Save the topic section.
6. In the Files area of your site create a folder home_images and upload all the images to that folder.
7. With a bit of luck it will work.
hth