Awesome

cool-php-captcha

⚠️This project is not maintained anymore.⚠️

I suggest use a modern and secure alterative, for example: reCAPTCHA.

This is the official GitHub project from code.google.com/p/cool-php-captcha

This project generates friendly captcha images. This project provides the SimpleCaptcha class. Some fetures are: Background and foreground colors, dictionary words, non-dictionary random words, blur, shadows, JPEG and PNG support.

Basic example

session_start();
$captcha = new SimpleCaptcha();
// Change configuration...
//$captcha->wordsFile = null;           // Disable dictionary words and use random letters instead
//$captcha->wordsFile = 'words/es.txt'; // Enable spanish words dictionary
//$captcha->session_var = 'secretword'; // Changes the session variable from 'captcha' to 'secretword'
$captcha->CreateImage();

... will output an image, for example: <br>

You can validate the php captcha with: (case-insensitive version)

if (empty($_SESSION['captcha']) || strtolower(trim($_REQUEST['captcha'])) != $_SESSION['captcha']) {
    return "Invalid captcha";
}

You can see a live example here: http://joserodriguez.cl/cool-php-captcha

More examples

Background and foreground colors, dictionary words, non-dictionary random words, blur, shadows, JPEG and PNG support:<br> <br> <img src='http://cool-php-captcha.googlecode.com/files/examples.jpg' />