<?php

if(get_post_meta( get_the_ID(), "portfolio-lightbox", true ) == '1') {

    $link = esc_url(wp_get_attachment_url( get_post_thumbnail_id() ));
    $title = esc_attr(get_the_title());
    $class = ' class="prettyPhoto" ';
    $rel = ' rel="prettyPhoto[portfolio]" ';
    $meta = $class. $rel;

} else {

    $link = esc_url(get_permalink());
    $title = esc_attr(get_the_title());
    $meta = '';

}

return '<a href="'. $link .'" title="'. $title .'" . $meta .>....</a>';