randimg.php

<?php
$dirname = $_SERVER['DOCUMENT_ROOT'].'/';
$dir = opendir($dirname);

while($file = readdir($dir)) {
	if($file != '.' && $file != '..' && $file != 'index.php')
	{
		//echo '<a href="'.$file.'">'.$file.'</a>';
		$filelist[] = $file;
	}
}

closedir($dir);

$countimg = count($filelist);
$randimg = mt_rand(0, $countimg-1);

echo '<img src="'.$filelist[$randimg].'" alt="Cool story bro" />';

?>