How to retrieve a previously submitted job

webthumb.php

<?php
try {
    $webthumb = new Bluga_Webthumb();
    $webthumb->setApiKey($APIKEY);
    $job = $webthumb->addUrl($url,'medium2', 1024, 768);
    $job->options->notify = "Your notify url";
    $webthumb->submitRequests();

    // save the job to retrieve it later
    file_put_contents('/tmp/thumbjob.txt', serialize($job));

    // later in the notified scripts
    $theJob = unserialize(file_get_contents('/tmp/thumbjob.txt'));
    $webthumb = new Bluga_Webthumb();
    $webthumb->setApiKey($APIKEY);
    $webthumb->addJob($job);
    $webthumb->fetchToFile($job, '/tmp/image.png');

} catch (Exception $e) {
    var_dump($e->getMessage());
}
?>