QR code shortcode for wordpress

gistfile1.php

<?php
    function qr($atts, $content=null) {
        extract(shortcode_atts( array('url' => ''), $atts));
        $googleurl = 'https://chart.googleapis.com/chart?chs=250x250&cht=qr&chl=' . urlencode($url);
        return '<img src="' . $googleurl . '" />';
    }
    add_shortcode('qr', 'qr');
?>