Easy. Go here:
http://ma.tt/scripts/randomimage/
and create your script.
Create a new forum block (html)
and simply link to it there per the tutorial.
Be sure the images are set to the size parameters for your blocks.
^nevermind that.You can specify the width in the image html,below is 200 pixels for example
Code:
<image src="http://yoursite/something/rotate.php" width="200">