php实现页面直接下载图片

$mime = 'application/force-download';
            header('Pragma: public'); // required
            header('Expires: 0'); // no cache
            header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
            header('Cache-Control: private',false);
            header('Content-Type: '.$mime);
            header('Content-Disposition: attachment; filename="'.basename($file_name).'"');
            header('Content-Transfer-Encoding: binary');
            header('Connection: close');
            readfile($file_name); // push it out
            exit();