link to parent album

At the moment it is supported to "link to image page", I would like to add "link to parent album" to it.

I'm a programmer, but I'm absolutely new to the Drupal API.

if ($link == 'node') {
  $output .= l($img_tag, 'node/'. $node->nid, array(), NULL, NULL, FALSE, TRUE);
}

I guess it's pretty simple. I need to refer to the parent node and not to the node id as described here, and I need to add this option to the possibilities of $link on other places in the code. If someone can tell me how to refer to that parent node, I can already test it in my own code :)