Read all sub directories within a certain folder to display a random image

I have this code i have been using....but i need a conditional where it will read all the sub directories of /bg to select an image as opposed to a specific folder if they were on a subpage.

Heres my code so far which works perfectly for all subpages to display specific images:

//This would tell us its on the homepage if it helps:
$this->level() == 0

//This is the code so far
$path = '/home/sites/mydomain.co.uk/public_html/public/images/bg/'.$this->slug;


$homepagefile = URL_PUBLIC.'public/images/bg/'.$this->slug.'/main.jpg';

$bgimagearray = array();
$iterator = new DirectoryIterator($path);
foreach ($iterator as $fileinfo) {
    if ($fileinfo->isFile() && !preg_match('\.jpg$/', $fileinfo->getFilename())) {
        $bgimagearray[] = "'" . $fileinfo->getFilename() . "'";
    }
}

$bgimage = array_rand($bgimagearray);

?>

<div id="bg">
    <div>
        <table cellspacing="0" cellpadding="0">
            <tr>
                <td><img src="<?php echo $file.trim($bgimagearray[$bgimage], "'"); ?>" alt=""/></td>
            </tr>
        </table>
    </div>
</div>

Any help would be appreciated, im sure its not rocket science but ive tried a few ways and cant get my head around it.

Thanks in advance.

This is what I 've come up with. Haven't tested it though...

<?php
$isHome = $this->level() == 0

$path = '/home/sites/mydomain.co.uk/public_html/public/images/bg/';
if (!$isHome) $path .= $this->slug;

$homepagefile = URL_PUBLIC.'public/images/bg/'.$this->slug.'/main.jpg';

$bgimagearray = array();
$iterator = new DirectoryIterator($path);
foreach ($iterator as $fileinfo) {
    if ($fileinfo->isFile() && !preg_match('\.jpg$/', $fileinfo->getFilename()) &&  !$isHome) {
        $bgimagearray[] = "'" . $fileinfo->getFilename() . "'";
    } else if ($fileinfo->isDir() && $isHome) {
        $iterator2 = new DirectoryIterator($path . $fileinfo->getFilename());
        foreach ($iterator2 as $fileinfo2) {
            if ($fileinfo2->isFile() && !preg_match('\.jpg$/', $fileinfo2->getFilename())) {
                $bgimagearray[] = "'" . $fileinfo->getFilename() . '/' . $fileinfo2->getFilename() . "'";
            }
        }
    }
}

$bgimage = array_rand($bgimagearray);

?>

<div id="bg">
    <div>
        <table cellspacing="0" cellpadding="0">
            <tr>
                <td><img src="<?php echo $file.trim($bgimagearray[$bgimage], "'"); ?>" alt=""/></td>
            </tr>
        </table>
    </div>
</div>

$Directory = new RecursiveDirectoryIterator($path);
$Iterator = new RecursiveIteratorIterator($Directory);
$Images = new RegexIterator($Iterator, '/^.+\.jpg$/i', RecursiveRegexIterator::GET_MATCH);

foreach ($Images as $pathname) {
    $bgimagearray[] = $pathname;
}

edit: My mistake, the regular expression must match the whole path, not just the extension. And after filtering with RegexIterator, the value is just the path, not a fileinfo object. I've edited the above code to fix it. I tested this with PHP 5.3.2.