So in one of my recent projects I had to parse a Flickr feed and extract the image urls the code I came up with is as follows:

<?php
/* Author: Samuel Haddad
 * SimpleXML Flicker Feed Parser
 */
//Feed URL in RSS Format
$url ="http://api.flickr.com/services/feeds/photos_public.gne?lang=en-us&format=rss_200"; //FEED URL

//Use simple XML to parse the feed
$xml = simplexml_load_file($url);
$items = $xml->xpath('/rss/channel/item');
foreach($items as $item){
 $nsmedia = $item->children('http://search.yahoo.com/mrss/');
 $img = $nsmedia->content->attributes();
 echo $img; //URL of Image
 echo "<br/>";
}
?>

Of course my code did more then just extract the URL, but I will leave the rest up to the creative developers.