Sorry for pulling up an old post but I was searching for a random image script and found this post.
The ALA randomiser is pretty cool and has a few ideas i hadn't thought about so i ended up modifying it for my own needs.
To answer the original posters query and pass on information to others.
To randomise multiple images at the same time change the line
$imageNumber = time() % count($fileList);
with something like
$imageNumber = rand(0,(count($fileList) -1));
The original uses the time to choose which picture to pull up which is a good idea for a one off, but since the code is simple and will be executed within 1 second each time its called it will have the same (so-called) random number
