Hey I went through a few of the suggestions for having random images show up on the blog and I couldnt find anything that fit my needs. I found this really simple scrcipt you can use.

<?php

/*
* Name your images 1.jpg, 2.jpg etc.
*
* Add this line to your page where you want the images to 
* appear: <?php include "randomimage.php"; ?>
*/ 

// Change this to the total number of images in the folder
$total = "11";

// Change to the type of files to use eg. .jpg or .gif
$file_type = ".jpg";

// Change to the location of the folder containing the images
$image_folder = "images/random";

// You do not need to edit below this line

$start = "1";

$random = mt_rand($start, $total);

$image_name = $random . $file_type;

echo "<img src=\"$image_folder/$image_name\" alt=\"$image_name\" />";

?>

i am no php guru, just trying to give back a little.
credit for this goes to:
http://www.totallyphp.co.uk/scripts/random_image.htm

cheers!