使用 php DOM 抓取图像网址

php DOM的小问题。

<?php
    $url = "http://www.dogpile.com/search/images?q=" . rawurlencode($_GET['q']);
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
    curl_setopt($ch, CURLOPT_FOLLOWLOCATION, TRUE);
    curl_setopt($ch, CURLOPT_MAXREDIRS, 3);
    curl_setopt($ch, CURLOPT_USERAGENT, "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.13) Gecko/20080311 Firefox/2.0.0.13");
    curl_setopt($ch, CURLOPT_HEADER, FALSE);
    curl_setopt($ch, CURLOPT_TIMEOUT, 20);
    $output = curl_exec($ch);
    curl_close($ch);
    $dom = new DOMDocument;
    $dom->loadHTML($output);
    print_r($dom->getElementById('imageResults'));
?>

我正在尝试从结果中获取缩略图和完整图像网址。但我无法获取所需的信息...