<ol>
<li>Get a <a href="http://www.flickr.com/services/api/keys/">Flickr API Key and Secret</a> from Flickr for this Moodle site.</li>
<li>Enter those details here, then click Save and then Settings to come back to this page.  You will see that Moodle has generated a callback URL for you.</li>
<li>Edit your <a href="http://www.flickr.com/services/api/keys/">Flickr</a> key details again and set the callback URL.</li></ol>