integrate form validation and captcha helper

[eluser]B3geN14S[/eluser]
[quote author="treenef" date="1403702768"]What I do is generate a random four digit number using the random library.

Then in the controller I set this in a session. When the form is submitted I check the session matches the input text.

Code:

$random = "2839";  <- store this in a session

$vals = array(
      'word'  => $random,
      'img_path'  => path-to-captcha/',
      'img_url'  => base_url().'path-to-captcha/',
      'font_path'  => 'path-to-font.ttf',
      'img_width'  => '150',
      'img_height' => 30,
      'expiration' => 300
  );

[/quote]

Thanks for the option you proposed, treenef!
Since this is my first project with CodeIgniter, could you provide some sample code to make it clearer to me?