Motivated by this: http://stackoverflow.com/questions/6953833/using-googleviewer-for-displaying-documents-in-the-localhost/6954278#6954278 here is how you can take your public ip in php

public-ip.php

<?php

/**
 * Retrieve public ip with PHP cURL
 */
$curl_handle=curl_init();
curl_setopt($curl_handle,CURLOPT_URL,'http://whatismyip.org/');
curl_setopt($curl_handle,CURLOPT_RETURNTRANSFER,1);
curl_setopt($curl_handle,CURLOPT_CONNECTTIMEOUT,2);
$public_ip = curl_exec($curl_handle);
curl_close($curl_handle);

echo "my ip address is ".$public_ip;

/**
 * It works as long as whatsmyip.org is up and running.
 * We get the public ip address even if we call the script
 * from it's public ip, localhost, 127.0.0.* or it's lan ip.
 */
?>