RSS Feeds and image extraction indepth

Question

Hi all, I have spent time trying to solve this problem and this is as far as ive got. basically im trying to pull images from rss feeds. i use magpie to process the feeds as shown below.. this snippet is within a class

function getImagesUrl($str) {
    $a = array();
    $pos = 0;
    $topos;
    $init = 1;

    while($init) {
        $pos = strpos($str, "img",  $pos);
        if($pos != FALSE) {
            $topos = strpos($str, ">", $pos);
            $imagetag = substr($str, $pos, ($topos - $pos));
            $url = $this->getImageUrl($imagetag);
            $pos = $topos;
            array_push($a, $url);
        }
        else {
            $init = 0;
        }
    }
    return $a;
}


/*
 * get the full url inside src atribute in <img>
*/
function getImageUrl($image) {
    $p = strpos($image, "src=", 0);
    $p+= 5; // remove o src="
    $tp = strpos($image, '" ', $p);
    $str = substr($image, $p, ($tp - $p));
    return $str;
}                

using the above functions... i call them this way... so far this outputs the data i'll paste later on

            @$rss = fetch_rss($rsso->url);
            if (@$rss)
                {
                $items=$rss->items;
                  foreach ($items as $item ) 
                    {
                    if (isset($item['title'])&&isset($item['description']))
                        {
                    $hash=md5($this->es($item['title']).$this->es($item['description']));
                     $content = $item['content'];
                    foreach($content as $c) {
                        // get the images on content
                        $arr = $this->getImagesUrl($c);
                        print_r($arr);
                        }

here is an example of output

 1. Array ( [0] =>
    http://api.tweetmeme.com/imagebutton.gif?url=http://mashable.com/2010/09/25/trailmeme/
    [1] =>
    http://cdn.mashable.com/wp-content/plugins/wp-digg-this/i/gbuzz-feed.png
    [2] =>
    http://mashable.com/wp-content/plugins/wp-digg-this/i/fb.jpg
    [3] =>
    http://mashable.com/wp-content/plugins/wp-digg-this/i/diggme.png
    [4] =>
    http://ec.mashable.com/wp-content/uploads/2009/01/bizspark2.gif
    [5] =>
    http://cdn.mashable.com/wp-content/uploads/2010/09/web.png
    [6] =>
    http://mashable.com/wp-content/uploads/2010/09/Screen-shot-2010-09-24-at-10.51.26-PM.png
    [7] =>
    http://cdn.mashable.com/wp-content/uploads/2009/02/bizspark.jpg
    [8] =>
    http://feedads.g.doubleclick.net/~at/lxx00QTjYBaYojpnpnTa6MXUmh4/0/di
    [9] => [10] =>
    http://feedads.g.doubleclick.net/~at/lxx00QTjYBaYojpnpnTa6MXUmh4/1/di
    [11] => [12] =>
    http://feeds.feedburner.com/~ff/Mashable?i=0N_mvMwPHYk:j5Pmi_N-JQ8:D7DqB2pKExk [13] => [14] =>
    http://feeds.feedburner.com/~ff/Mashable?i=0N_mvMwPHYk:j5Pmi_N-JQ8:V_sGLiPBpWU [15] => [16] =>
    http://feeds.feedburner.com/~ff/Mashable?i=0N_mvMwPHYk:j5Pmi_N-JQ8:F7zBnMyn0Lo [17] => [18] =>
    http://feeds.feedburner.com/~ff/Mashable?d=qj6IDK7rITs
    [19] => [20] =>
    http://feeds.feedburner.com/~ff/Mashable?d=_e0tkf89iUM
    [21] => [22] =>
    http://feeds.feedburner.com/~ff/Mashable?i=0N_mvMwPHYk:j5Pmi_N-JQ8:gIN9vFwOqvQ [23] => [24] =>
    http://feeds.feedburner.com/~ff/Mashable?d=yIl2AUoC8zA
    [25] => [26] =>
    http://feeds.feedburner.com/~ff/Mashable?d=P0ZAIrC63Ok
    [27] => [28] =>
    http://feeds.feedburner.com/~ff/Mashable?d=I9og5sOYxJI
    [29] => [30] =>
    http://feeds.feedburner.com/~ff/Mashable?d=CC-BsrAYo0A
    [31] => [32] =>
    http://feeds.feedburner.com/~ff/Mashable?i=0N_mvMwPHYk:j5Pmi_N-JQ8:_cyp7NeR2Rw [33] => [34] =>
    http://feeds.feedburner.com/~r/Mashable/~4/0N_mvMwPHYk
    )

is there a way i can filter out the correct url for image? for example.... i would like to strip out urls with no extensions of "jpg,png,gif" etc. secondly, i would like to scrap urls with eg bizspark, digg, facebook, tweet, twitter etc. anybody found any easier way of doing this? please help me out