captcha web API

I know how everyone here loves APIs :bad:,
but I came across a web based API, that could
be very useful in certain situations.

A captcha - (login, designed to prevent automated spam
by offering a human readable image pattern which needs to
be keyed in for access).

This captcha API is made available with only a few lines of code.
I tried it, and it worked exactly as expected.

Here is the sample script:

<?

session_start();

// You need a unique string that identifies the user. The easiest way is to

// simply use the session ID. But because sending session IDs to other servers

// can be a security problem, we use only a part of the session ID here.

// This is still a quasi-unique string, so it works just as well.

$captcha_id = substr(session_id(), 0, 15); // first 15 characters of the session ID

?>


<html><head></head><body>

<img src="http://captchator.com/captcha/image/<?= $captcha_id ?>" />

<br />

Please enter the text from the picture:

<form action="test.php" method="post">

<input type="text" name="captcha_answer" />

<input type="submit" name="submit" value="Check" />

</form>


<?

if ($_POST['captcha_answer']) {

  // remove anything except letters and numbers (security)

  $answer = preg_replace('/[^a-z0-9]+/i', '', $_POST['captcha_answer']);

  // check answer

  // if you get an error message because your provider has diabled allow_url_fopen,

  // please use the myfile() function from the following website instead of file():

  // http://www.klamm.de/crashforum/showpost.php?p=1041750&postcount=5

  if (implode(file("http://captchator.com/captcha/check_answer/".$captcha_id."/".$answer)) == '1') {

    echo '<div style="color: green">Answer correct!</div>';

  } else {

    echo '<div style="color: red">Wrong answer, please try again.</div>';

  }

}

?>


<p>

See the <a href="test.php.txt">source code</a> of this script.

</p>


</body></html>

Here is the sample script loaded:

Posted Image

This is after I entered the proper code:

Posted Image

This is after I entered an improper code:

Posted Image

No difficult code here, just a simple API which is easily incorporated.

Not for everyone, but in the right situation, it could be very helpful
in the never ending fight against spam prevention.

References:
Captchator - Captcha service for PHP, Ruby on Rails, Python, ...