<?php
  //Generates a security code within the session file.  Used with function captcha_form()
  function secure_code() {
    $string = str_replace("O","Z",str_shuffle(rand(1,9).chr(rand(65,90)).rand(1,9).chr(rand(65,90)).rand(1,9).chr(rand(65,90))));
    if ((time()-$_SESSION['secure_code_life']) > 4||!$_SESSION['secure_code_life']) {
      $_SESSION['secure_code'] = $string;
      $_SESSION['secure_code_life'] = time();
    }
  }

  //Shows the html which is a image tag and input box, this is to be used within an existing form tag
  function captcha_form() {
    global $err;

    secure_code();
    $form = '<img id="secure" src="/img.php?secure=1" /><br />
                  <input type="text" name="secure" size="6" maxlength="6">'.$err['secure'].' <b>&#171; Enter the code seen in the image above.</b><br>
                  Click <a href="javascript:redraw_secure()">here to redraw</a> the security code if it is not readable.<br>
                  If the security code does not redraw <a href="'.$_SERVER['SCRIPT_NAME'].($_SERVER['QUERY_STRING']?'?'.$_SERVER['QUERY_STRING']:'').'">refresh this page</a>.<br>
                  It should be <b>six</b> alphanumeric characters.
                  <script type="text/javascript">function redraw_secure() {if (document.getElementById) {if (document.getElementById("secure")) {document.getElementById("secure").src="/img.php?secure=2&r="+Math.random();}}}</script>';
    return $form;
  }
?>

<?php
  //The below code should be located in a separate file called img.php within the root directory (unless you change the path in function captcha_form())
  header("Content-type: image/png");

  if ($_GET['secure']=='2') secure_code(); //regenerate the code, used in redraw js function in captcha_form()
  //the glob functiton here is just grabbing a collection of background images designed to randomize/obscure the security code a little
  //this background could just as well be generated at random during runtime though
  $background = glob(ini_get('doc_root').'images/security*.jpg');
  $background = $background[rand(0,count($background)-1)];
  $im = imagecreatefromjpeg($background);

  $color = imagecolorallocate($im, rand(0,255), rand(0,255), rand(0,255));
  $px = rand(imagesx($im)-250,imagesx($im)-80);
  $py = rand(imagesy($im)-10,imagesy($im)-20);
  //Randomizing the fonts used and the sizes, these are true type fonts and PHP is located on a windows machine in this example
  $fonts = array($_SERVER['windir'].'/fonts/impact.ttf',
                $_SERVER['windir'].'/fonts/ariblk.ttf',
                $_SERVER['windir'].'/fonts/breakaway.ttf',
                $_SERVER['windir'].'/fonts/bricklet.ttf');
  $font = $fonts[rand(0,count($fonts)-1)];
  $fontsize = rand(13,20);
  $angle = rand(-15,15);

  //Write the security code to the image and output the image
  imagettftext($im,$fontsize,$angle,$px,$py,$color,$font,$_SESSION['secure_code']);
  imagepng($im);
  imagedestroy($im);

?>