<?php

$directory = "./01/";
$namePattern = _o.jpg
$miniaturePattern = "_o-lightbox.jpg";

$images = glob($directory . "*".$namePattern);


foreach($images as $image):
?>
   <li><a href="<?php echo $image; ?>" class="html5lightbox"><img src="<?php echo str_replace($namePattern, $miniaturePattern, $image); ?>"/></a></li>
<?php endforeach; ?>