Create post QR Code using Google Charts

functions.php

/**
 * Return a QR Code
 */
function get_the_QRcode($postID = 0, $size ='150', $evLevel='L', $margin='0') 
{
    global $post;
    
    if ( is_null($postID) ) {
        $postID = $post->ID;
    }

    $url = urlencode( get_permalink($postID) );

    return '<img src="http://chart.apis.google.com/chart?chs=' . $size . 'x' . $size . '&cht=qr&chld=' . $evLevel . '|' . $margin . '&chl=' . $url . '" alt="QR code" width="' . $size . '" height="' . $size . '"/>';
}

/**
 * Echo a QR Code
 */
function the_QRcode($postID = 0, $size ='150', $evLevel='L', $margin='0') 
{
    echo get_the_QRcode($postID, $size, $evLevel, $margin);
}

single.php

<?php the_QRcode() ?>