$re = '/http:\/\/url.com\/wp-content\/uploads\/\S+(?<!150x150)\.(?:jpg|jpeg|png|gif)/m';
$str = 'http://url.com/wp-content/uploads/2009/09/name-of-the-file-150x150.png
http://url.com/wp-content/uploads/2009/09/name-of-the-file-1324x130.png';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php