Forum OpenACS Q&A: Captchas for the register form

I want to share something we have been using for some time to generate a captcha image in the user registration form.

We use the ImageMagick library with the TclMagick interface to create an image, based of a background image, and then we write some random text on it, you can see how this working in (https://oacsrocks.org/register/user-new )

ImageMagick comes pre-installed in many linux distributions and TclMagick is usually not hard to get (out from repositories or compiled from source) or even you can get a really simple build from pragana.net http://www.pragana.net/tclmagick-simple-build.tar.gz

First you will need some images for use as backgrounds and place them in some public directory, for example the first time I did this the backgrounds and generated captchas went to  /myserverroot/www/captchas

I made a little zip with some background images and the captchas-proc.tcl file, I usually place this file under the acs-subsite/tcl/ directory.

here is the zip:

Then we edited the file at /acs-subsite/lib/user-new.tcl and added this ad_page_contract

ad_page_contract {
register form with captchas
} {
    {captcha_id {[captcha::create]} }
}

Then we extended the register form with this new couple of fields, the captcha_id and the captcha_text:

ad_form -extend -name register -form {
    {captcha_id:text(hidden) {value $captcha_id }  {after_html "<td>&nbsp;</td><td><img src=[captcha::get_filename $captcha_id] ></td>" } }
    {captcha_text:text {label "Enter the text above"} }
}

The database table for the captchas is very simple, we use a definition like this:

create table captchas
(
captcha_id integer default nextval('captcha_seq'),
captcha_file varchar(200),
captcha_text varchar(20),
primary key (captcha_id)
);

with a sequence for the captcha_id

CREATE SEQUENCE captcha_seq;

I hope this helps someone, any doubts, comments, corrections and tips for improvement will be greatly appreciated.

Your approach to generate image captchas to openacs forms is very easy to implement. I just downloaded tclmagick simple build from Praganas' website as you suggested and unzipped it inside tcldir in my linux box.

The only additional step i did was create a validation block for ad_form in the tcl page script:

} -validate {captcha_text
{[captcha::validate $captcha_id $captcha_text]}
"Text must match!"
}
}

It works fine!

My only concern with this approach is inaccessibility of image CAPTCHA to users who are blind, have low vision, or have a learning disability such as dyslexia.

My question is: are you working on some kind of alternative to image captchas like audio CAPTCHAs or other? Maybe it could be a good openacs web accessibility project for google summer of code 2007 (see http://www.openacs.org/xowiki/GSoC).

Alternatives to image captchas see this W3C paper:

http://www.w3.org/TR/turingtest/

Here in Brazil one of our federal universities - Universidade Federal do Rio de Janeiro - is developing a software called SINAL - Sistema Interativo de Navegação no Linux (Linux Interactive Navigation System) to enable web accessibility to users who are blind. SINAL is going to use MBROLA as far as i know.

link to MBROLA voices database:
http://tcts.fpms.ac.be/synthesis/mbrola/mbrcopybin.html

link to MBROLA project website:
http://tcts.fpms.ac.be/synthesis/mbrola.html

I have been improving the captcha script a little bit, now it doesnt requires any use of database and the images have moved to a more standard location because it seems this will be integrated to openacs in a not so distant future.

Now there is no need to add tables to the database, but TclMagick is still required. The image con enabled/disabled with a parameter.

The zip contains:

The directory captchas, with some background images (this directory is expected to be placed on /acs-subsite/www/shared because the procs default to that location)

the file captcha-procs.tcl

A file, acs-subsite.diff, this needs to be applied to the acs-subsite package, the changes are:

- adds a new parameter to the acs-subsite.info file.
- Adds the necessary lines to /acs-subsite/lib/user-new.tcl for the captchas to work.

-------------------------

Entry for this subject on the bugTracker: https://openacs.org/bugtracker/openacs/bug?bug%5fnumber=3088

yes, TclMagick "should" work without Tk installed or X11, but I haven't been able to make it work that way neither.

for using the pragana simple build of Tcl-magick, yes, you will need ImageMagick installed, and its libraries installed in something like /usr/lib/libMagick.so.7