<?
class CaptchaSecurityImages {
 
   var $font;
   var $code;
 
   function generateCode($characters) {
      /* list all possible characters, similar looking characters and vowels have been removed */
      $possible = '23456789';
      $code = '';
      $i = 0;
      while ($i < $characters) { 
         $code .= substr($possible, mt_rand(0, strlen($possible)-1), 1);
         $i++;
      }
      return $code;
   }
 
   function CaptchaSecurityImages($width='120',$height='40',$characters='6') {
      $this->font = dirname(__FILE__) . '/c.ttf';
      $this->code = $this->generateCode($characters);

      /* insert the code into a cookie */
      /* one-way encrypt the code, using the first two characters from the code */
      $dstat = stat(dirname(__FILE__));
      setcookie("_c", crypt(crypt("$this->code", substr("$this->code", 0, 2)), "" . $dstat['mtime']), 0, "/");

      /* font size will be 75% of the image height */
      $font_size = $height * 0.75;
      $image = @imagecreate($width, $height) or die('Cannot initialize new GD image stream');
      /* set the colours */
      $background_color = imagecolorallocate($image, 255, 255, 255);
      $text_color = imagecolorallocate($image, 0, 0, 0);
      $noise_color = imagecolorallocate($image, 100, 120, 180);
      /* generate random dots in background */
      for( $i=0; $i<($width*$height)/3; $i++ ) {
         imagefilledellipse($image, mt_rand(0,$width), mt_rand(0,$height), 1, 1, $noise_color);
      }
      /* generate random lines in background */
      for( $i=0; $i<($width*$height)/150; $i++ ) {
         imageline($image, mt_rand(0,$width), mt_rand(0,$height), mt_rand(0,$width), mt_rand(0,$height), $noise_color);
      }
      /* create textbox and add text */
      $textbox = imagettfbbox($font_size, 0, $this->font, $this->code) or die('Error in imagettfbbox function');
      $x = ($width - $textbox[4])/2;
      $y = ($height - $textbox[5])/2;
      imagettftext($image, $font_size, 0, $x, $y, $text_color, $this->font , $this->code) or die('Error in imagettftext function');
      /* output captcha image to browser */
      header('Content-Type: image/jpeg');
      header("Cache-Control: no-cache, must-revalidate"); // HTTP/1.1
      header("Expires: Sat, 26 Jul 1997 05:00:00 GMT"); // Date in the past
      imagejpeg($image);
      imagedestroy($image);
   }
 
}
$captcha = new CaptchaSecurityImages(120, 40, 6);
?>