The Captcha Class

<?php
    class Captcha {
        var $width = 60;
        var $height = 20;
        var $img = null;
        var $chars = 6;
        var $fontsize = 5;
        var $sessionvar = 'captcha';
         
        function __construct() {
            session_start();
        }
         
        function run() {
            $this->outputImage();
        }
         
        function check($arr) {
            if (isset($arr) && is_array($arr)) {
                if (isset($arr[$this->sessionvar])) {
                    if ($arr[$this->sessionvar] == $_SESSION[$this->sessionvar]) {
                        return true;
                    }
                }
            }
        }
         
        function randomString($length = 6) {
            $chars = "abcdefghijklmnopqrstuvwxyz0123456789";
            for ($i = 0; $i < $length; $i++) {
                $string .= $chars[mt_rand(0, strlen($chars)-1)];
            }
            return $string;
        }
         
        function outputImage() {
            $this->img = ImageCreate ($this->width, $this->height);
            if ($this->img) {
                header("Content-type: image/png"); 
                 
                $bg = ImageColorAllocate($this->img, 255, 255, 255); 
                $txt = ImageColorAllocate($this->img, 0, 0, 0); 
                 
                $string = $this->randomString($this->chars);
                 
                ImageString($this->img, 31, $this->fontsize, 0, $string, $txt);
                Imagepng($this->img); 
                 
                $_SESSION[$this->sessionvar] = $string; 
            }
        }
    }
?>

The class has two main functions, run() and check() – The run function will output an image so make sure the HTML image tag is linked to the file where you use the run() function. Examples below.

Showing the Image

include('captcha.php');
$captcha = new Captcha;
$captcha->run();

If you name that file cimage.php you can embed it into forms in the following way:

<img class="lazyload" src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsQAAA7EAZUrDhsAAAANSURBVBhXYzh8+PB/AAffA0nNPuCLAAAAAElFTkSuQmCC" data-original="cimage.php" alt="Human Verification" /> <input type="text" name="captcha" id="captcha" />

Checking the code

Wherever your form is submitting to is where you should be checking the code. This can either be in the same file or an external file. The following code will allow you to check the $_POST array and make sure the user has entered the correct code.

include('captcha.php');
$captcha = new Captcha;
 
if ($captcha->check($_POST)) {
    echo 'Correct Code';
} else {
    echo 'Invalid Code';
}