CAPTCHA validation

[eluser]someone [/eluser]
Hello,

I have created some form for inserting data into database and for checking if the data was sent from human I have used CAPTCHA which is already integrated to CI.

This is my controller:

Code:

$this->load->helper('captcha');
    
    $checkrules = array(
     'img_path' => realpath(APPPATH . '../upload/checking/img') . '/',
     'img_url' => base_url() . 'upload/checking/img/',
     'font_path' => realpath(APPPATH . '../upload/checking/font.ttf'),
     'img_width' => 150,
     'img_height' => 30,
     'expiration' => 7200
    );
    
    $check = create_captcha($checkrules);
    $data['checkimg'] = $check['image'];
          
    $this->form_validation->set_rules('name', 'Name', 'required|max_length[40]|xss_clean');
    $this->form_validation->set_rules('email', 'E-mail', 'required|valid_email|xss_clean');
    $this->form_validation->set_rules('website', 'Website', 'max_length[80]|prep_url|xss_clean');
    $this->form_validation->set_rules('comment', 'Comment', 'required|xss_clean');
    $this->form_validation->set_rules('check', 'Check', 'required|xss_clean');
          
    if ($this->form_validation->run() == FALSE)
    {
     $this->load->view('cms/theme', $data);
    }
    else
    {
     echo "success";
     $this->load->view('cms/theme', $data);
    }

My question now is what's the best way to validate CAPTCHA?
1.) Creating callback, which I have already done, but there was problem because when I send form is error with new CAPTCHA code.

2.) Inserting CAPTCHA's code into database and check from it. Problem is because there will be a lot of loading database and it will be very busy.

And second question. Is this CAPTCHA saving only .jpg pictures in folder or it can be any other format there? (I'm asking this because I want to delete this captcha's after they are used.)

Thanks in advance! :-)