phpqrcode不能输出二维码

header('Content-Type: image/png');
include_once 'phpqrcode/qrlib.php';
$a = "http://www.play17.cn/play/wlogin.html";
ob_clean();
QRcode::png($a);

加入输出类型

header('Content-Type: image/png');

清除缓存ob_clean()

ob_clean();