This is what I tried but can't get it print value of src
 $dom = new domDocument;
    /*** load the html into the object ***/
    $dom->loadHTML($html);
    /*** discard white space ***/
    $dom->preserveWhiteSpace = false;
    /*** the table by its tag name ***/
    $images = $dom->getElementsByTagName('img');
    /*** loop over the table rows ***/
    foreach ($images as $img)
    {
        /*** get each column by tag name ***/
        $url = $img->getElementsByTagName('src');
        /*** echo the values ***/
        echo $url->nodeValue;
        echo '<hr />';
    }
EDIT: I solved this problem
$dom = new domDocument;
/*** load the html into the object ***/
$dom->loadHTML($string);
/*** discard white space ***/
$dom->preserveWhiteSpace = false;
$images = $dom->getElementsByTagName('img');
foreach($images as $img)
    {
        $url = $img->getAttribute('src');   
        $alt = $img->getAttribute('alt');   
        echo "Title: $alt<br>$url<br>";
    }