php 二维码加水印图片 支持ios,android,win8

    $logo = 'logo.png';

    if(is_file($logo))
    {
        $QR = imagecreatefromstring(file_get_contents($filename));
        $logo = imagecreatefromstring(file_get_contents($logo));
        $QR_width = imagesx($QR);
        $QR_height = imagesy($QR);
        $logo_width = imagesx($logo);
        $logo_height = imagesy($logo);
        $logo_qr_width = $QR_width / 5;
        $scale = $logo_width / $logo_qr_width;
        $logo_qr_height = $logo_height / $scale;
        $from_width = ($QR_width - $logo_qr_width) / 2;
        imagecopyresampled($QR, $logo, $from_width, $from_width, 0, 0, $logo_qr_width, $logo_qr_height, $logo_width, $logo_height);
        imagepng($QR,$filename);
    }