<?php
$article = '<img src="http://php.net/images/logo.php">';
$match = preg_match(
// Match the src attribute with the opening quote.
'/src=(?\'quote\'["\'])'
// Match the URL for the image.
. '([\S\s]+?)\.(png|gif|jpeg)'
// Re-use the opening quote as closing quote.
. '(?P=quote)/m',
$article,
$matches
);
var_dump($match, $matches);