<?php
// list of possible variables containing user's IP
$_SERVER['HTTP_X_FORWARDED_FOR'];
$_SERVER['HTTP_X_FORWARDED'];
$_SERVER['HTTP_FORWARDED_FOR'];
$_SERVER['HTTP_FORWARDED'];
$_SERVER['HTTP_X_COMING_FROM'];
$_SERVER['HTTP_COMING_FROM'];
$_SERVER['HTTP_CLIENT_IP'];
$_SERVER['HTTP_VIA'];
$_SERVER['REMOTE_ADDR'];
?>

$_SERVER["HTTP_REFERER"] 

/*
 * Name: Get IP (RFC 1918 compliant)
 * Developer: Bob Wilson (TWI)
 * Creation Date: 5 April, 2003
 * © 2003 by The Whole Internet, LLC
 */

// Access this function (in calling file) by either of the following methods:
// 1. Set variable, eg, $ip=getIP()...then echo, print or test $ip further
// 2. Echo or print function directly...W/O QUOTES (single or double)

function getIP() {
  $octet = explode(".", $_SERVER['HTTP_CLIENT_IP']);
  $refer = explode(".", $_SERVER['REMOTE_ADDR']);
  // check if HTTP_CLIENT_IP same as REMOTE_ADDR
  // if not, reverse array order of entire octet
  if (!empty($refer[0]) && ($refer[0] != $octet[0])) {
    $octet = array_reverse($octet);
  } // endif array compare
  // ternaries to eliminate private addresses, as per rfc1918
  $priv1 = (!empty($octet[0]) && ($octet[0] != 10)) ? 1 : 0;
  $priv2 = ($octet[0] != 172) || ($octet[1] < 16) || ($octet[1] > 31) ? 1 : 0;
  $priv3 = ($octet[0] != 192) || ($octet[1] < 168) ? 1 : 0;
  if ($priv1 && $priv2 && $priv3 != 0) {
    return implode('.',$octet);
  } elseif (!empty($_SERVER['HTTP_X_FORWARDED_FOR'])) {
    return $_SERVER['HTTP_X_FORWARDED_FOR'];
  } else {
    return $_SERVER['REMOTE_ADDR'];
  } unset($octet, $refer);
}