Help adding a href link to php code on my post template

hi i am using custom fields to display a series of images in my modified post template and i cant seem to fugure out how to add the <a href= html tag to open the images in a lightbox when user clicks on it.

here is my code:
<h3>My Photos</h3>
<div id=”thumnail_class”>
<div class=”thumnail_class”>
<?php foreach($thumbnails as $user_submit_image){echo ‘<img src=”‘ . $user_submit_image . ‘” alt=”” rel=”lightbox” />’ ;} ?>
</div></div>

Does anyone know where to add the html link code? i have tried many variations but no luck. Any help would be great appreciated.