Main Class: hn_captcha (hn_captcha.class.php)

/**
  * PHP-Class hn_captcha Version 1.4, released 04-Oct-2007
  *
  * Author: Horst Nogajski, coding@nogajski.de
  *
  * $Id: shortinfo.php,v 1.2 2009/03/25 11:52:10 horst Exp $
  *
  * Download: http://hn273.users.phpclasses.org/browse/package/1569.html
  *
  * License: GNU LGPL (http://www.opensource.org/licenses/lgpl-license.html)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with this library; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
  *
  **/


/**
  * This class generates a picture to use in forms that perform CAPTCHA test
  * (Completely Automated Public Turing to tell Computers from Humans Apart).
  * After the test form is submitted a key entered by the user in a text field
  * is compared by the class to determine whether it matches the text in the picture.
  *
  * The class is a fork of the original released at www.phpclasses.org
  * by Julien Pachet with the name ocr_captcha.
  *
  * The following enhancements were added:
  *
  * - Support to make it work with GD library before version 2
  * - Hacking prevention
  * - Optional use of Web safe colors
  * - Limit the number of users attempts
  * - Display an optional refresh link to generate a new picture with a different key
  *   without counting to the user attempts limit verification
  * - Support the use of multiple random TrueType fonts
  * - Control the output image by only three parameters: number of text characters
  *   and minimum and maximum size preserving the size proportion
  * - Preserve all request parameters passed to the page via the GET method,
  *   so the CAPTCHA test can be added to existing scripts with minimal changes
  * - Added a debug option for testing the current configuration
  *
  * All the configuration settings are passed to the class in an array when the object instance is initialized.
  *
  * The class only needs two function calls to be used: display_form() and validate_submit().
  *
  * The class comes with examplefiles.
  * If you don't have it: http://hn273.users.phpclasses.org/browse/package/1569.html
  *
  * ----------------------------------------------------------------------------
  *
  * HISTORY
  *
  *
  * changes in version 1.1:   (2004-April-16)
  *
  *  - added a new configuration-variable: maxrotation
  *
  *  - added a new configuration-variable: secretstring
  *
  *  - modified function get_try(): now ever returns a string of 16 chars
  *____
  *
  *
  * changes in version 1.2:   (2004-April-19)
  *
  *  - added a new configuration-variable: secretposition
  *
  *  - once more modified the function get_try(): generate a string of 32 chars length,
  *    where at secretposition is the number of current-try.
  *    Hopefully this is enough for hackprevention.
  *____
  *
  *
  * changes in version 1.3:   (2006-April-11)
  *
  *  - fixed a security-hole, what was discovered by Daniel Jagszent. Many thank's for
  *    testing, fixing and sharing it, Daniel!
  *    He has tested the class in a modified way, like it is described here:
  *    http://www.puremango.co.uk/cm_breaking_captcha_115.php
  *    It was possible to manually do the captcha-test, notice the public and private keys.
  *    In automated way this keys could send as long as the image-file exists!
  *    (with different other datas and independent from the new captcha-string!)
  *____
  *
  *
  * changes in version 1.4:   (2007-October-04)
  *
  *   - fixed get_gd_version to check extension_loaded and get the version directly from GD-library. (no more use of php_info())
  *     ( thanks to Jari Turkia and others )
  *
  *   - added display_form_part function. The general idea is to use HN-captcha as a part of an existing form.
  *     A new examplefile comes with the package therefor: hn_captcha.example_formpart.php
  *     ( thanks to Jari Turkia and all people who have posted to the supportforum )
  *
  *   - fixed use of Debug. Added param for DebugSwitch to constructor now.
  *     ( reported from and thanks to Mist Hill )
  *
  *   - added the ability to automatically scan the TTF_folder for available '.ttf'-files.
  *     To use this, you have to set the var TTF_range to (string)'AUTO', instead of passing and array with filenames.
  *     ( thanks to cYbercOsmOnauT (Tekin) )
  *
  *   - added new boolean Configuration-Param: use_only_md5
  *     If is set to TRUE, we only use chars 0-9 and A-F for Keygeneration,
  *     if is set to FALSE, the default, we use 2-9 (without 8) and A-Z (without B I O).
  *     Small range we get with md5($str), wide range we get with base64_encode(md5($str))
  *
  *   - modified the private key generator (function generate_private()) to replace some chars that may confuse the users, especially when using stylized fonts.
  *     ( thanks to Bill Price )
  *
  *   - added new string Configuration-Param: form_action_method
  *     Is only needed when working with function "Display_Form_Part".
  *     Value can be 'POST' or 'GET', default is 'POST'.
  *
  *   - added some Languages:
  *     - Italian,   Andrea Nicaretta
  *     - French,    Benoit Dausse
  *     - Finnish,   Jari Turkia
  *     ( thank you )
  *
  *   - packed some TrueTypeFonts for the package:
  *     - get them here: http://nogajski.de/horst/php/captcha/fonts.zip
  *       and unpack them with subfolder to the hn_captcha folder. Then the
  *       examples should run directly!
  *     - they are all from Tom7: http://fonts.tom7.com/
  *       please read his License http://fonts.tom7.com/legal/ or http://fonts.tom7.com/legal/readme.txt
  *       (the file is included in fonts-dir, too)
  *       ( many thanks Tom! )
  *
  *  ... and few other little changes and sanitizing.
  *
  *  ( ... and many thanks to all the people who have send me mails with nice words or ascii-art =:) )
  *____
  *
  **/