Math captcha for anonymous users
Heine —Sat, 2007/02/24 - 12:58
This morning I broke down and wrote a simple math captcha module (for Drupal) to use with user registration and anonymous commenting on this site.
Because this site uses caching for anonymous users, the module needs to make sure that whenever a captcha is displayed, the page is not added to the cache.
Caching is handled by includes/common.inc:
if (variable_get('cache', 0)) {
page_set_cache();
}
module_invoke_all('exit');
}
So whenever a captcha is added to a form (hook_form_alter), we simply set the global cache variable to FALSE.
// ...
$GLOBALS['conf']['cache'] = FALSE;
This certainly has drawbacks, but those are mitigated when the comment form is displayed on a seperate page.
To bad that math captcha's are easy to bypass or break by simple trial and error or automated calculation.
The module can be downloaded from my public Subversion repository. See also Adding settings to Captcha.