Add Captcha in Codeigniter

Write this code inside a function of Controller

                 $vals = array(

        //'word'          => 'Random word',
        'img_path'      => 'assets/captcha/',
        'img_url'       => base_url().'assets/captcha/',
        'font_path'     => 'system/fonts/texb.ttf',
        'img_width'     => '150',
        'img_height'    => 30,
        'expiration'    => 7200,
        'word_length'   => 6,
        'font_size'     => 16,
        'img_id'        => 'Imageid',
        'pool'          => '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ',

        // White background and border, black text and red grid
        'colors'        => array(
        'background' => array(255, 255, 255),
        'border' => array(255, 255, 255),
        'text' => array(0, 0, 0),
        'grid' => array(255, 40, 40)
        )
);

$cap = create_captcha($vals);
$data['cap_image'] = $cap['image'];
//$this->session->unset_userdata('scaptcha');
$this->session->set_userdata('scaptcha',$cap['word']);



$this->load->view('templates/header');
$this->load->view('users/register', $data);
$this->load->view('templates/footer');

Inside View file

                                  <p id="cap_img"><?php echo $cap_image; ?></p>
<p>Can't read the image? click <a href="javascript:void(0);" class="refreshCaptcha">here</a> to refresh.</p>



<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

<!-- captcha refresh code -->
<script>
$(document).ready(function(){
    $('.refreshCaptcha').on('click', function(){
    $.ajax({
    url : "<?php echo base_url().'users/refresh'; ?>",
    method  : "post",
    success:function(data){
    $('#cap_img').html(data);
    }

    })
       
    });
});
</script>

Inside Controller file

                    public function refresh(){
        // Captcha configuration

        $vals = array(
        //'word'          => 'Random word',
        'img_path'      => 'assets/captcha/',
        'img_url'       => base_url().'assets/captcha/',
        'font_path'     => 'system/fonts/texb.ttf',
        'img_width'     => '150',
        'img_height'    => 30,
        'expiration'    => 7200,
        'word_length'   => 6,
        'font_size'     => 16,
        'img_id'        => 'Imageid',
        'pool'          => '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ',

        // White background and border, black text and red grid
        'colors'        => array(
        'background' => array(255, 255, 255),
        'border' => array(255, 255, 255),
        'text' => array(0, 0, 0),
        'grid' => array(255, 40, 40)
        )
);
        $captcha = create_captcha($vals);
       
        // Unset previous captcha and set new captcha word
        $this->session->unset_userdata('scaptcha');
        $this->session->set_userdata('scaptcha',$captcha['word']);
       
        // Display captcha image
        echo $captcha['image'];