WP: Auto extract the first image from the post content

gistfile1

// AUTOMATICALLY EXTRACT THE FIRST IMAGE FROM THE POST 
function getImage($num) {
    global $more;
    $more = 1;
    $link = get_permalink();
    $content = get_the_content();
    $count = substr_count($content, '<img');
    $start = 0;
    for($i=1;$i<=$count;$i++) {
        $imgBeg = strpos($content, '<img', $start);
        $post = substr($content, $imgBeg);
        $imgEnd = strpos($post, '>');
        $postOutput = substr($post, 0, $imgEnd+1);
        $postOutput = preg_replace('/width="([0-9]*)" height="([0-9]*)"/', '',$postOutput);;
        $image[$i] = $postOutput;
        $start=$imgEnd+1;
    }
    if(stristr($image[$num],'<img')) { echo '<a href="'.$link.'">'.$image[$num]."</a>"; }
    $more = 0;
}