reCaptcha

February 6 2009

Putting together a decent captcha solution by-hand can be quite a bit of work. So why not simplify the whole process and re-use an existing solution like reCaptcha? They do a really good job of managing this service for you (and it's totally free).

Step 1: Download

Download the reCaptcha library (reCaptcha calls them plugins) from the reCaptcha website.
Note: I used the PHP library

Step 2: Install

Place the reCaptcha library some place on your webserver where you can include it into your PHP form.

Step 3: Register

You can't use reCaptcha without a registered API key so you'll have to register for one. Don't worry, it's free.

Step 4: Code

Build a PHP form that includes the reCaptcha library so that you can test out your account to make sure it's working. You can use the following PHP code:

standalone.php

<?php



include('recaptchalib.php');



$challenge = (isset($_POST["recaptcha_challenge_field"]) ? $_POST["recaptcha_challenge_field"] : null);

$response = (isset($_POST["recaptcha_response_field"]) ? $_POST["recaptcha_response_field"] : null);

$publickey = 'your_public_key';

$privatekey = 'your_private_key';

$result = '';



if (($challenge != null) && ($response != null)){

  $test = recaptcha_check_answer($privatekey, $_SERVER['REMOTE_ADDR'], $challenge, $response);

  if ($test->is_valid) $result = 'Congratulations! You appear to be human ... <input type="submit" value="try again"/>';

  else $result = recaptcha_get_html($publickey, $test->error) . '<br/><input type="submit" value="test"/>';

} else {

  $result = recaptcha_get_html($publickey) . '<br/><input type="submit" value="test"/>';

}



?>

<form method="post" action="<?php echo $_SERVER['REQUEST_URI']; ?>">

  <?php echo $result; ?>

</form>

Step 5: Test

Load up your new PHP form and try it out. It should work like this one.