如何使用url从任何网站获取图像

I need to get image url only from any webpage with php nothing else.how can i get image url please help.

I have try file_get_contents(url); but its not usefull for me.

Thanks in advance

$url="http://example.com";
$html = file_get_contents($url);
$doc = new DOMDocument();
@$doc->loadHTML($html);
$tags = $doc->getElementsByTagName('img');
foreach ($tags as $tag) {
echo $tag->getAttribute('src');
}

Check this code its working for me.