<?php
$s = 'http://d...content-available-to-author-only...n.com/uploads/image1.jpg|||http://d...content-available-to-author-only...n.com/uploads/image2.jpg|||http://d...content-available-to-author-only...n.com/uploads/image3.jpg|||...';
$result = explode('|||', $s, 2);
echo $result[0];
?>