title: Change text and background color in reCaptcha image
body: <p>I'm using a reCaptcha class (the one that's included in the <a href="http://www.konyukhov.com/soft/tank_auth/" rel="nofollow">Tank Auth</a> authentication library for Codeigniter) and wanted to know if it's possible to change the background and text color of the image reCaptcha returns?</p>
  
  <p>Here is the actual reCaptcha Helper PHP code included with Tank Auth:</p>
  
  <pre><code>&lt;?php
  /*
   * This is a PHP library that handles calling reCAPTCHA.
   *    - Documentation and latest version
   *          http://recaptcha.net/plugins/php/
   *    - Get a reCAPTCHA API Key
   *          http://recaptcha.net/api/getkey
   *    - Discussion group
   *          http://groups.google.com/group/recaptcha
   *
   * Copyright (c) 2007 reCAPTCHA -- http://recaptcha.net
   * AUTHORS:
   *   Mike Crawford
   *   Ben Maurer
   *
   * Permission is hereby granted, free of charge, to any person obtaining a copy
   * of this software and associated documentation files (the "Software"), to deal
   * in the Software without restriction, including without limitation the rights
   * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
   * copies of the Software, and to permit persons to whom the Software is
   * furnished to do so, subject to the following conditions:
   *
   * The above copyright notice and this permission notice shall be included in
   * all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
   * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
   * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
   * THE SOFTWARE.
   */
  
  /**
   * The reCAPTCHA server URL's
   */
  define("RECAPTCHA_API_SERVER", "http://api.recaptcha.net");
  define("RECAPTCHA_API_SECURE_SERVER", "https://api-secure.recaptcha.net");
  define("RECAPTCHA_VERIFY_SERVER", "api-verify.recaptcha.net");
  
  /**
   * Encodes the given data into a query string format
   * @param $data - array of string elements to be encoded
   * @return string - encoded request
   */
  function _recaptcha_qsencode ($data) {
          $req = "";
          foreach ( $data as $key =&gt; $value )
                  $req .= $key . '=' . urlencode( stripslashes($value) ) . '&amp;';
  
          // Cut the last '&amp;'
          $req=substr($req,0,strlen($req)-1);
          return $req;
  }
  
  
  
  /**
   * Submits an HTTP POST to a reCAPTCHA server
   * @param string $host
   * @param string $path
   * @param array $data
   * @param int port
   * @return array response
   */
  function _recaptcha_http_post($host, $path, $data, $port = 80) {
  
          $req = _recaptcha_qsencode ($data);
  
          $http_request  = "POST $path HTTP/1.0\r\n";
          $http_request .= "Host: $host\r\n";
          $http_request .= "Content-Type: application/x-www-form-urlencoded;\r\n";
          $http_request .= "Content-Length: " . strlen($req) . "\r\n";
          $http_request .= "User-Agent: reCAPTCHA/PHP\r\n";
          $http_request .= "\r\n";
          $http_request .= $req;
  
          $response = '';
          if( false == ( $fs = @fsockopen($host, $port, $errno, $errstr, 10) ) ) {
                  die ('Could not open socket');
          }
  
          fwrite($fs, $http_request);
  
          while ( !feof($fs) )
                  $response .= fgets($fs, 1160); // One TCP-IP packet
          fclose($fs);
          $response = explode("\r\n\r\n", $response, 2);
  
          return $response;
  }
  
  
  
  /**
   * Gets the challenge HTML (javascript and non-javascript version).
   * This is called from the browser, and the resulting reCAPTCHA HTML widget
   * is embedded within the HTML form it was called from.
   * @param string $pubkey A public key for reCAPTCHA
   * @param string $error The error given by reCAPTCHA (optional, default is null)
   * @param boolean $use_ssl Should the request be made over ssl? (optional, default is false)
  
   * @return string - The HTML to be embedded in the user's form.
   */
  function recaptcha_get_html ($pubkey, $error = null, $use_ssl = false)
  {
      if ($pubkey == null || $pubkey == '') {
          die ("To use reCAPTCHA you must get an API key from &lt;a href='http://recaptcha.net/api/getkey'&gt;http://recaptcha.net/api/getkey&lt;/a&gt;");
      }
  
      if ($use_ssl) {
                  $server = RECAPTCHA_API_SECURE_SERVER;
          } else {
                  $server = RECAPTCHA_API_SERVER;
          }
  
          $errorpart = "";
          if ($error) {
             $errorpart = "&amp;amp;error=" . $error;
          }
          return '&lt;script type="text/javascript" src="'. $server . '/challenge?k=' . $pubkey . $errorpart . '"&gt;&lt;/script&gt;
  
      &lt;noscript&gt;
          &lt;iframe src="'. $server . '/noscript?k=' . $pubkey . $errorpart . '" height="300" width="500" frameborder="0"&gt;&lt;/iframe&gt;&lt;br/&gt;
          &lt;textarea name="recaptcha_challenge_field" rows="3" cols="40"&gt;&lt;/textarea&gt;
          &lt;input type="hidden" name="recaptcha_response_field" value="manual_challenge"/&gt;
      &lt;/noscript&gt;';
  }
  
  
  
  
  /**
   * A ReCaptchaResponse is returned from recaptcha_check_answer()
   */
  class ReCaptchaResponse {
          var $is_valid;
          var $error;
  }
  
  
  /**
    * Calls an HTTP POST function to verify if the user's guess was correct
    * @param string $privkey
    * @param string $remoteip
    * @param string $challenge
    * @param string $response
    * @param array $extra_params an array of extra variables to post to the server
    * @return ReCaptchaResponse
    */
  function recaptcha_check_answer ($privkey, $remoteip, $challenge, $response, $extra_params = array())
  {
      if ($privkey == null || $privkey == '') {
          die ("To use reCAPTCHA you must get an API key from &lt;a href='http://recaptcha.net/api/getkey'&gt;http://recaptcha.net/api/getkey&lt;/a&gt;");
      }
  
      if ($remoteip == null || $remoteip == '') {
          die ("For security reasons, you must pass the remote ip to reCAPTCHA");
      }
  
  
  
          //discard spam submissions
          if ($challenge == null || strlen($challenge) == 0 || $response == null || strlen($response) == 0) {
                  $recaptcha_response = new ReCaptchaResponse();
                  $recaptcha_response-&gt;is_valid = false;
                  $recaptcha_response-&gt;error = 'incorrect-captcha-sol';
                  return $recaptcha_response;
          }
  
          $response = _recaptcha_http_post (RECAPTCHA_VERIFY_SERVER, "/verify",
                                            array (
                                                   'privatekey' =&gt; $privkey,
                                                   'remoteip' =&gt; $remoteip,
                                                   'challenge' =&gt; $challenge,
                                                   'response' =&gt; $response
                                                   ) + $extra_params
                                            );
  
          $answers = explode ("\n", $response [1]);
          $recaptcha_response = new ReCaptchaResponse();
  
          if (trim ($answers [0]) == 'true') {
                  $recaptcha_response-&gt;is_valid = true;
          }
          else {
                  $recaptcha_response-&gt;is_valid = false;
                  $recaptcha_response-&gt;error = $answers [1];
          }
          return $recaptcha_response;
  
  }
  
  /**
   * gets a URL where the user can sign up for reCAPTCHA. If your application
   * has a configuration page where you enter a key, you should provide a link
   * using this function.
   * @param string $domain The domain where the page is hosted
   * @param string $appname The name of your application
   */
  function recaptcha_get_signup_url ($domain = null, $appname = null) {
      return "http://recaptcha.net/api/getkey?" .  _recaptcha_qsencode (array ('domain' =&gt; $domain, 'app' =&gt; $appname));
  }
  
  function _recaptcha_aes_pad($val) {
      $block_size = 16;
      $numpad = $block_size - (strlen ($val) % $block_size);
      return str_pad($val, strlen ($val) + $numpad, chr($numpad));
  }
  
  /* Mailhide related code */
  
  function _recaptcha_aes_encrypt($val,$ky) {
      if (! function_exists ("mcrypt_encrypt")) {
          die ("To use reCAPTCHA Mailhide, you need to have the mcrypt php module installed.");
      }
      $mode=MCRYPT_MODE_CBC;   
      $enc=MCRYPT_RIJNDAEL_128;
      $val=_recaptcha_aes_pad($val);
      return mcrypt_encrypt($enc, $ky, $val, $mode, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0");
  }
  
  
  function _recaptcha_mailhide_urlbase64 ($x) {
      return strtr(base64_encode ($x), '+/', '-_');
  }
  
  /* gets the reCAPTCHA Mailhide url for a given email, public key and private key */
  function recaptcha_mailhide_url($pubkey, $privkey, $email) {
      if ($pubkey == '' || $pubkey == null || $privkey == "" || $privkey == null) {
          die ("To use reCAPTCHA Mailhide, you have to sign up for a public and private key, " .
               "you can do so at &lt;a href='http://mailhide.recaptcha.net/apikey'&gt;http://mailhide.recaptcha.net/apikey&lt;/a&gt;");
      }
  
  
      $ky = pack('H*', $privkey);
      $cryptmail = _recaptcha_aes_encrypt ($email, $ky);
  
      return "http://mailhide.recaptcha.net/d?k=" . $pubkey . "&amp;c=" . _recaptcha_mailhide_urlbase64 ($cryptmail);
  }
  
  /**
   * gets the parts of the email to expose to the user.
   * eg, given johndoe@example,com return ["john", "example.com"].
   * the email is then displayed as john...@example.com
   */
  function _recaptcha_mailhide_email_parts ($email) {
      $arr = preg_split("/@/", $email );
  
      if (strlen ($arr[0]) &lt;= 4) {
          $arr[0] = substr ($arr[0], 0, 1);
      } else if (strlen ($arr[0]) &lt;= 6) {
          $arr[0] = substr ($arr[0], 0, 3);
      } else {
          $arr[0] = substr ($arr[0], 0, 4);
      }
      return $arr;
  }
  
  /**
   * Gets html to display an email address given a public an private key.
   * to get a key, go to:
   *
   * http://mailhide.recaptcha.net/apikey
   */
  function recaptcha_mailhide_html($pubkey, $privkey, $email) {
      $emailparts = _recaptcha_mailhide_email_parts ($email);
      $url = recaptcha_mailhide_url ($pubkey, $privkey, $email);
  
      return htmlentities($emailparts[0]) . "&lt;a href='" . htmlentities ($url) .
          "' onclick=\"window.open('" . htmlentities ($url) . "', '', 'toolbar=0,scrollbars=0,location=0,statusbar=0,menubar=0,resizable=0,width=500,height=300'); return false;\" title=\"Reveal this e-mail address\"&gt;...&lt;/a&gt;@" . htmlentities ($emailparts [1]);
  
  }
  
  
  ?&gt;
  </code></pre>