MODX snippet to generate a phpthumb sized random image from a given directory.

randomImage.php

<?php
/* 
  Requirements: MODX, phpthumbof
*/
$folder	= 'img/random/';  // change to your random img dir
$height	= 120;            // desired height in px
$width	= 940;            // desired width in px
$crop	= 'C';            // zoom crop where? T,R,B,L,C (top,right,bottom,left,center)

// space seperated list of extensions
$exts = 'jpg jpeg png';

$files = array(); $i = -1;
if ('' == $folder) $folder = './';

$handle = opendir($folder);
$exts = explode(' ', $exts);
while (false !== ($file = readdir($handle))) {
    foreach($exts as $ext) { // for each extension check the extension
        if (preg_match('/\.'.$ext.'$/i', $file, $test)) { // faster than ereg, case insensitive
            $files[] = $file; // it’s good
            ++$i;
        }
    }
}
closedir($handle); // we’re not using it anymore
mt_srand((double)microtime()*1000000); // seed for PHP < 4.2
$rand = mt_rand(0, $i); // $i was incremented as we went along

// feed it to phpthumbof
$output = $modx->runSnippet('phpthumbof',array(
        'input' => $folder.$files[$rand],
        'options' => '&w='.$width.'&h='.$height.'&zc='.$crop.'&aoe=0&far=0'
));

// output
echo '<img src="'.$output.'" alt="" />';

//?>