Daniel Davies writes "textTHaCAA - Text (Telling Humans and Computers Apart Automatically)
a way of telling if the submitter of a web form is human or a bot by getting them to answer a simple random question in an accessible way.
textTHaCAA is an automated system for Telling Humans and Computers Apart Automatically that was inspired by CAPTCHA from Carnegie Mellon however unlike those problems which can be difficult for people with certain disabilities for example those who are blind or visually impaired and need to use a screen reader to enable them to browse the web textTHaCAA is designed to be accessible to all users and achieves this by asking simple randomly generated text based multiple choice questions where the user has to select the members of one group from a list randomly selected from members of a series of different groups.
textTHaCAA can help on websites in many ways some examples for uses of it include
- prevent automatic signing up for accounts on things such as mailing lists and forums
- stop bots using forms on your website for such purposes as comment spam.
- avoid the problem of bots rigging polls and votes
examples of it in use can be seen on this website when you try to add a comment to anything on the site, click here for an example.
the code generated by the system validates cleanly against XHTML 1.0 Strict
the textTHaCAA library has been open sourced under the LGPL and is written completely in PHP meaning it can with a little programming ability be integrated relatively easily into other packages written in PHP
the textTHaCAA library can be downloaded from here"