$re = '/(\d+)[\w-]+\.jpg/';
$str = '101018-202x300.jpg
100116-215x300.jpg
1000748-300x157.jpg
100138-196x300.jpg
100308-companion-in-surgical-studies-208x300.jpg
100463-Ambroise-Pare-300x216.jpg
100523-Grulee-collection-pediatrics-194x300.jpg';
preg_match_all($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