capcha.php

<?php

function generateRandomString($length,$characters) {
  $random_string = '';
  for ($i = 0; $i < $length; $i++) {
    $random_string .= $characters[rand(0, strlen($characters) - 1)];
  }
  return $random_string;
}

function makeCaptcha($text) {
  if ($text != null) {
    $image_height = 70;
    $image_width = 280;
    $text_font = "./tny.ttf";
    $text_size = 40;
    $text_angle = 0;
    $text_x = 55 + rand(-50,50);
    $text_y = 55;
    $image = imagecreate($image_width, $image_height);
    $background_color = imagecolorallocate($image, 0xff, 0xff, 0xff);

    // randomize each character's size, orientation, & color
    for ($i = 0; $i < strlen($text); $i++) {
      $rand_x = $text_x + $text_size*(7/10)*$i + rand(-1,4);
      $rand_y = $text_y + rand(-5,5);
      $rand_angle = rand(-10,10);
      $rand_size = $text_size + rand(-10,20);
      $rand_r = rand(-50,50);
      $rand_g = rand(-50,50);
      $rand_b = rand(-50,50);
      $rand_color = imagecolorallocate($image, $rand_r, $rand_g, $rand_b);
      imagettftext($image, $rand_size, $rand_angle, $rand_x, $rand_y, $rand_color, $text_font, $text[$i]);
    }

    // we distort the image by drawing $num_lines horizontal lines
    // that are the same color as the background
    // and then apply a convolution matrix
    $num_lines = 20;
    for ($i = 0; $i < $num_lines; $i++) {
      $rand_y1 = rand(0,$image_height);
      $rand_y2 = rand(0,$image_height);
      imageline($image,0,$rand_y1,$image_width,$rand_y2,$background_color);
    }
    return $image;
  } else {
    return false;
  }
}

function gaussianBlur($image, $num = 1) {
  $gaussian = array(array(1.0, 2.0, 1.0), array(2.0, -1.0, 2.0), array(1.0, 2.0, 1.0));
  for ($i = 0; $i < $num; $i++) {
    imageconvolution($image, $gaussian, 12, 0);  
  }
  return $image;
}

if(isset($_GET['printpic'])) {
  $captcha = makeCaptcha($_SESSION['captcha']);
  $captcha = gaussianBlur($captcha,1);
  Header('Content-type: image/png');
  imagepng($captcha);
  imagedestroy($captcha);
}

?>