captcha modify six letters - php

Question

i have following captcha code:
<?php
class CaptchaView extends View
{
private $fontsDir = 'captcha_resources/fonts/';
private $backgroundsDir = 'captcha_resources/backgrounds/';
private static $dirCache = array();
public function render($controller)
{
$code = $controller->viewVars["code"];
/**
* The next part is orginnaly written by ted from mastercode.nl and modified for using in this mod.
**/
header("content-type:image/png");
header('Cache-control: no-cache, no-store');
$width = 100;
$height = 30;
$img = imagecreatefrompng(self::backgroundImage());
// add noise
for ($i = 0; $i < 1; $i++) {
$horizontal_progress = 0;
$vertical_pos = rand(1, $height / 2);
do {
$horizontal_step_size = floor(rand(1, $width / 5));
imageline($img, $horizontal_progress, $vertical_pos, ($horizontal_progress += $horizontal_step_size), ($vertical_pos = rand(1, $height)), self::color("tekst"));
} while ($horizontal_progress < $width);
}
$background = imagecolorallocate($img, self::color("bg"), self::color("bg"), self::color("bg"));
for ($g = 0; $g < 30; $g++) {
$t = rand(10, 20);
$t = $t[0];
$ypos = rand(0, $height);
$xpos = rand(0, $width);
$kleur = imagecolorallocate($img, self::color("bgtekst"), self::color("bgtekst"), self::color("bgtekst"));
imagettftext($img, self::size(), self::move(), $xpos, $ypos, $kleur, self::font(), $t);
}
$stukje = $width / (strlen($code) + 3) + 5;
for ($j = 0; $j < strlen($code); $j++) {
$tek = $code[$j];
$ypos = rand(23, 27);
$xpos = $stukje * ($j + 1) - 5;
$color2 = imagecolorallocate($img, self::color("tekst"), self::color("tekst"), self::color("tekst"));
imagettftext($img, self::size(), self::move(), $xpos, $ypos, $color2, self::font(), $tek);
}
imagepng($img);
imagedestroy($img);
}
/**
* Some functions :)
* Also orginally written by mastercode.nl
**/
/**
* Function to create a random color
* #auteur mastercode.nl
* #param $type string Mode for the color
* #return int
**/
private static function color($type)
{
switch ($type) {
case "bg":
$color = rand(224, 255);
break;
case "tekst":
$color = rand(0, 127);
break;
case "bgtekst":
$color = rand(200, 224);
break;
default:
$color = rand(0, 255);
break;
}
return $color;
}
/**
* Function to ranom the size
* #auteur mastercode.nl
* #return int
**/
private static function size()
{
return rand(18, 22);
}
/**
* Function to random the posistion
* #auteur mastercode.nl
* #return int
**/
private static function move()
{
return rand(-22, 22);
}
/**
* Function to return a ttf file from fonts map
* #auteur mastercode.nl
* #return string
**/
function randomFileByExt($dir, $ext)
{
$f = opendir($dir);
if (empty(self::$dirCache[$dir])) {
$ar = array();
while (($file = #readdir($f)) !== false) {
if (!in_array($file, array('.', '..')) && substr_compare($file, $ext, -strlen($ext)) == 0) {
$ar[] = $file;
}
}
self::$dirCache[$dir] = $ar;
} else {
$ar = self::$dirCache[$dir];
}
if (count($ar)) {
$i = rand(0, (count($ar) - 1));
return $dir . $ar[$i];
}
}
private function backgroundImage()
{
return self::randomFileByExt(Config::get("VIEWS_PATH") . $this->backgroundsDir, ".png");
}
private function font()
{
return self::randomFileByExt(Config::get("VIEWS_PATH") . $this->fontsDir, ".ttf");
}
}
actually it display 4 letters with a disturbed background
i want block some spam bot them i think to modify code to increase security increasing number of letters
can you tell me how to modify it to display 6 letters instead of 4?

Answer 1

1) Best solution is to implement existing Captcha like reCaptcha or so..
docs : http://code.google.com/intl/en_EN/apis/recaptcha/intro.html
PHP : http://code.google.com/intl/en_EN/apis/recaptcha/docs/php.html
2) To modify your code to push 6 instead of 4 letters edit part of code like this:
$stukje = $width / (strlen($code) + 5) + 5; //instead of "+3) +5;"
should do the trick, but I can't test it, since I don't know in which mod it was used (what CMS, PHP Framework,...)