A simple chess based captcha system written in php and javascript.
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assets Piece paths and fenchallenge session notice Nov 1, 2015
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Chess Captcha

Requirements: php >= 5.4, jquery > 1.8 | Latest Version 2.0.2

This is a captcha system where the user either recreates the position of the pieces on the board - non chess savvy users - or she solves a mate-in-one puzzle by putting the piece on the square where it gives the checkmate - chess savvy users only. There is also a no js fallback that exists mostly as a placeholder for future iterations; don't use it. Chesscaptcha was built for fun, it is a work in progress so feel free to make pull requests and contribute!

View demo here.

📚 Laravel + Chesscaptcha Tutorial here.

📚 Chess captcha + Emojis here.

Created by @elioair | twitter: @elioair

Libraries used:


Through Composer

composer require elioair/chesscaptcha

After composer finishes importing the package:

  • You may remove the /vendor/elioair/chesscaptcha/examples directory
  • Place the /vendor/elioair/chesscaptcha/assets directory or it's contents where it suits your project. Note that the image files are used both by the js client and the php server side.
  • Fix the image paths in the /vendor/elioair/chesscaptcha/src/ChessCaptcha/BoardImageCreator.php

Directly cloning the repo

Clone the repository and see immediately how it works by going to the /examples folder. You might need to require_once the files of the classes involved in the class files in the src/ChessCaptcha folder.

Quick tip: run composer install and then composer dump-autoload --optimize and include the loader.

Working Example: /examples/chesscaptcha-example.php

The php configuration

// The array that contains the configuration for the php side
  $config = [
    'matemode'=>'no', // yes or no
    'nojsfallback'=>'no', // yes or no; activate the fallback in case js is disabled
    'titleoverride'=>'Copy the position below', // text override
    'titlemateoverride'=>'Mate-In-One', // text override
    'helpoverride'=>'Drag the pieces into the board to copy the given position. To remove a piece drag it out of the board.', // text override
    'startoverride'=>'Start', // text override
    'clearoverride'=>'Clear', // text override
    'pieceStyle'=>'wikipedia', // the name of the piece style to use or 'random', default is 'wikipedia'

  $chesscaptcha = new \ChessCaptcha\ChessCaptcha($config['whitesquare'], $config['blacksquare'], $config['matemode'], $config['nojsfallback'], $config['pieceStyle']);


<form ...>
  <!-- The #chesscaptcha div where the captcha will be rendered. If needed you can change the # in the $config array -->
  <div id="chesscaptcha"><?php if($config['nojsfallback'] == 'yes'){ echo $chesscaptcha->noJsHtml($config['pieceImages']);}?></div>

  <input type="submit" id="submitform" value="Submit">

The javascript + js options object

// The object containing the configuration for the js side
var chessCaptchaParams = {
    cc_divId: '<?php echo $config['divId'];?>',
    cc_mateMode: '<?php echo $config['matemode']?>' === 'no' ? false : true,
    cc_whiteSquare: '<?php echo $config['whitesquare'];?>',
    cc_blackSquare: '<?php echo $config['blacksquare'];?>',
    cc_titleOverride: '<?php echo $config['titleoverride'];?>',
    cc_mateTitleOverride: '<?php echo $config['titlemateoverride'];?>',
    cc_helpOverride: '<?php echo $config['helpoverride'];?>',
    cc_startOverride: '<?php echo $config['startoverride'];?>',
    cc_clearOverride: '<?php echo $config['clearoverride'];?>',
    cc_sideToPlay: '<?php echo $chesscaptcha->chessCaptchaFenCode[2]; ?>',
    cc_challenge: '<?php echo $chesscaptcha->chessCaptchaChallenge; ?>',  // The image of the position
    cc_matechallenge: '<?php echo $chesscaptcha->chessCaptchaFenCode[0];?>',  // The fen code of matemode position
    cc_pathtoimg: '../assets/img/pieces',
    cc_piecestyle: '<?php echo $chesscaptcha->chessCaptchaPieceStyle;?>',
<script type="text/javascript" src="../assets/js/chesscaptcha.js"></script>
Add this at the end and configure it if you want ajax validation
<script type="text/javascript" src="../assets/js/chesscaptcha-ajax-validation.js"></script>


Grab the chesscaptchaposition from the POST request and feed it into the validation method. $validate = \ChessCaptcha\ChessCaptcha::validate($inputFen, $noJs, $colorTolerance); see the src/chesscaptchavalidate.php file for more.

Further Configuration:

Look into the boardimagecreator.php for settings on the image.


  • The position when set to Start from the button is not updated on purpose. Avoid having an initial position as a fen string in the fen array.

  • On some tablets, when zoomed-in the pieces are not placed correctly.


  • Add support for more than one instances per page.


1. How do I change the positions displayed?

Edit the array $givenFen in src/fengenerator.php for the simple mode and the $givenMateInOne for the mate mode.

2. Pieces are not showing up or no board image is shown.

Make sure that you have the paths to the image files of the pieces right. E.g. $pieceImageDir property in boardimagecreator.php and $config['$pieceImageDir'].

3. How do I make the check ignore the piece color?

Pass true as the third argument of the Chesscaptcha::validate method to make the comparison color agnostic.


Distributed under the MIT license