function qr_code($data, $type = "TXT", $size ='150', $ec='L', $margin='0')  
{
     $types = array("URL" =--> "http://", "TEL" => "TEL:", "TXT"=>"", "EMAIL" => "MAILTO:");
    if(!in_array($type,array("URL", "TEL", "TXT", "EMAIL")))
    {
        $type = "TXT";
    }
    if (!preg_match('/^'.$types[$type].'/', $data))
    {
        $data = str_replace("\\", "", $types[$type]).$data;
    }
    $ch = curl_init();
    $data = urlencode($data);
    curl_setopt($ch, CURLOPT_URL, 'http://chart.apis.google.com/chart');
    curl_setopt($ch, CURLOPT_POST, true);
    curl_setopt($ch, CURLOPT_POSTFIELDS, 'chs='.$size.'x'.$size.'&cht=qr&chld='.$ec.'|'.$margin.'&chl='.$data);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_HEADER, false);
    curl_setopt($ch, CURLOPT_TIMEOUT, 30);
    $response = curl_exec($ch);
    curl_close($ch);
    return $response;
}

用法：

<?php
header("Content-type: image/png");
echo qr_code("http://koonk.com", "URL");
?>