CAPTCHA plugin

This plugin implements a Completely Automated Public Turing test to tell Computers and Humans Apart also known as CAPTCHA.

Download the plugin using the plugin manager or manually from the following URL

• captcha-plugin-latest.tgz

• 03 Jan 17:12 - Moved some parts to a helper plugin for reuse in other plugins
• 16 Sep 18:40 - no longer rely on srand() which does not work on suhosin
• 15 Feb 21:57 - Czech language file
• 10 Dec 19:13 - French translation
• 14 Aug 04:49 - italian translation
• 14 Aug 04:46 - fixed encoding for german lang files
• 06 Aug 12:22 - upped the version string
• 04 Aug 07:32 - German Translation

• Needs the gd image library, on Ubuntu use sudo apt-get install php5-gd

The plugin provides four different methods of CAPTCHAs selectable in the config manager.

The first one (js) displays 5 random characters which need to be copied into an input box. This task is done through JavaScript automatically, then the whole CAPTCHA test is hidden from the user. Usual Spambots won't execute JavaScript or search the page for the characters, so this test should be quite effective without requiring any manual interaction from most users. The test is perfectly accessible for disabled users or users without JavaScript.

The second method (text) work just like the JavaScript method but without the automatic JavaScript. This will defeat SpamBots with enabled JavaScript but requires more interaction from users. It's still pretty simple to defeat by analyzing the page source. Accessibility is as good as with the first method.

The third method (image) finally does display the random chars as an automatically generated image. This test can not be defeated without using costly OCR techniques. Unfortunately this method effectively locks out blind users or users with textbrowsers. This feature needs the libGD PHP extension.

The fourth method (audio) improves the accessibility of the image CAPTCHA by adding a .wav download. The .wav file plays the letters of the CAPTCHA read in the NATO phonetical alphabet. Please note, that because of the way how the wave file is generated it might be easier to automatically decode than the image.

If you select the image type you may specify the size of the generated image. Larger images take more screen space and might be easier to recognize with OCR. On the other hand larger images are better to read for humans, too.

By default the CAPTCHA method is only applied for anonymous users. You may enable it for logged in users as well through the forusers option.

The CAPTCHA plugin not only protects the edit form but the user registration process, too. You can disable this through the regprotect option.

There has been some discussion that CAPTCHA doesn't go well the the Discussion plugin, but I found the latest version (discussion 08-08-2008) seems to work just fine. YMMV

— Could CAPTCHA be disabled for a certain IP or subnet and enabled for another? I might take a look at the code someday.

It would be useful to have temporary anonymous login (30min or so) after one CAPTCHA as it is in Wikipedia and as sudo acts in Ubuntu. it would solve the problem of comment vs edit CAPTCHA as well!

• would be nice to have a refresh button above the “listen” button that generates a new code, if the current is unreadable !
• would also be nice to have very easy to read CAPTCHAs, but that have easy arithmetic expression to calculate (like “1+4=” and the user must enter “5”), what do you think of it ?

When DokuWiki say that “most recent revision already exists” (not exactly, I have localized message) there is no CAPTCHA request on this page! This is true when “Use CAPTCHA for logged in users, too?” option enabled and when you need to restore old page revision. So, After enter CAPTCHA and pushing “Save” button for certain (old) revision “most recent revision exists” messages appears without CAPTCHA. You don't able to restore old page revision with “Use CAPTCHA for logged in users, too?” enabled.

In my case, all users are locked out as bots without even being presented with any CAPTCHA, regardless of whether Java is enabled in the browser. It could have something to do with mod_security or suhosin, but I haven't had time to persue it, and so removed the plugin as a temporary measure.