Jason A. Crome


CGI::Application::Plugin::CAPTCHA - Easily create, use, and verify CAPTCHAs in CGI::Application-based web applications.


Version 0.04


    # In your CGI::Application-based web application module. . .
    use CGI::Application::Plugin::CAPTCHA;

    sub setup
        my $self = shift;

        $self->run_modes([ qw/
            # Your other run modes go here

            IMAGE_OPTIONS    => {
                width    => 150,
                height   => 40,
                lines    => 10,
                font     => "/Library/Fonts/Arial",
                ptsize   => 18,
                bgcolor  => "#FFFF00",
            CREATE_OPTIONS   => [ 'ttf', 'rect' ],
            PARTICLE_OPTIONS => [ 300 ],

    # Create a run mode that calls the CAPTCHA creation method...
    sub create 
        my $self = shift;
        return $self->captcha_create;
    # In a template far, far away. . . 
    <img src="/delight/Ident/create"> (to generate a CAPTCHA image)

    # Back in your application, to verify the CAPTCHA...
    sub some_other_runmode
        my $self    = shift;
        my $request = $self->query;
        return unless $self->captcha_verify($request->cookie("hash"), $request->param("verify"));


CGI::Application::Plugin::CAPTCHA allows programmers to easily add and verify CAPTCHAs in their CGI::Application-derived web applications.

A CAPTCHA (or Completely Automated Public Turing Test to Tell Computers and Humans Apart) is an image with a random string of characters. A user must successfully enter the random string in order to submit a form. This is a simple (yet annoying) procedure for humans to complete, but one that is significantly more difficult for a form-stuffing script to complete without having to integrate some sort of OCR.

CAPTCHAs are not a perfect solution. Any skilled, diligent cracker will eventually be able to bypass a CAPTCHA, but it should be able to shut down your average script-kiddie.

CGI::Application::Plugin::CAPTCHA is a wrapper for GD::SecurityImage. It makes it more convenient to access GD::SecurityImage functionality, and gives a more CGI::Application-like way of doing it.

When a CAPTCHA is created with this module, raw image data is transmitted from your web application to the client browser. A cookie containing a checksum is also transmitted with the image. When the client submits their form for processing (along with their verification of the random string), captcha_verify() generates a checksum of the verification string the user entered. If the newly generated checksum matches the checksum found in the cookie, we trust that the CAPTCHA has been successfully entered, and we allow the user to continue processing their form.

The checksum is generated by taking the string in question, and joining it with a SECRET. We then generate an SHA1 hex digest of the resulting string. The end user will not be able to generate their own checksums to bypass the CAPTCHA check, because they do not know the value of our SECRET. This means it is important to choose a good value for your SECRET.

An easy way to generate a relatively good secret is to run the following perl snippet:

  perl -MDigest::SHA1=sha1_base64 -le 'print sha1_base64($$,time(),rand(9999))'

The author recognizes that the transmission of a cookie with the CAPTCHA image may not be a popular decision, and welcomes any patches from those who can provide an equally easy-to-implement solution.



This method is used to customize how new CAPTCHA images will be created. Values specified here are passed along to the appropriate functions in GD::SecurityImage when a new CAPTCHA is created.

It is recommended that you call captcha_config() in the cgiapp_init() method of your CGI::Application base class, and in the setup() method of any derived applications.

The following parameters are currently accepted:


This specifies what options will be passed to the constructor of GD::SecurityImage. Please see the documentation for GD::SecurityImage for more information.


This specifies what options will be passed to the create() method of GD::SecurityImage. Please see the documentation for GD::SecurityImage for more information.


This specifies what options will be passed to the particle() method of GD::SecurityImage. Please see the documentation for GD::SecurityImage for more information.


This specifies the secret that will be used when generating the checksum hash.


Creates the CAPTCHA image, and return a cookie with the encrypted hash of the random string. Takes no arguments.

The cookie created in this method is named hash, and contains only the encrypted hash. Future versions of this module will allow you to specify cookie options in greater detail.


Verifies that the value entered by the user matches what was in the CAPTCHA image. Argument 1 is the encrypted hash from the cookie sent by captcha_create(), and argument 2 is the value the user entered to verify the CAPTCHA image. Returns true if the CAPTCHA was successfully verified, else returns false.


Jason A. Crome, <cromedome@cpan.org>


  • Allow captcha_config() to take cookie configuration arguments.

  • Allow the plugin to actually create a run mode in your CGI::Application-based webapp without the developer having to manually create one.


Please report any bugs or feature requests to bug-cgi-application-plugin-captcha@rt.cpan.org, or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=CGI-Application-Plugin-CAPTCHA. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.


Patches, questions, and feedback are welcome.


A big thanks to Cees Hek for providing a great module for me to borrow code from (CGI::Application::Plugin::Session), to Michael Peters and Tony Fraser for all of their valuable input, and to the rest who contributed ideas and criticisms on the CGI::Application mailing list.

Additional thanks to chorny and Cees for the various bug fixes and patches they have submitted.


CGI::Application GD::SecurityImage Wikipedia entry for CAPTCHA - http://en.wikipedia.org/wiki/Captcha


Copyright 2005-2011 Jason A. Crome, all rights reserved.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.