$re = '/(?\'chemin\'(?|(^)|(.*\\\\)|(.*\/)|(^\/)))(?\'fichier\'(?\'prefix\'[a-z0-9_\-]{4})(?\'num_photo\'[0-9]{1,10})(?\'extention\'\.[a-z0-9]{3,4}))$/i';
$str = '/user/dd/MH105670.JPG';
preg_match($re, $str, $matches, PREG_OFFSET_CAPTURE, 0);
// Print the entire match result
var_dump($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