However, it only works with domains, not subdomains.

What do you mean? It shouldn't matter at all.

Anyway, try reCaptcha http://epapyr.us/recaptcha

The glitch occurs with registration. Can't generate key, as recaptcha can only use domain, not subdomain.

Have you ever changed $cookie_domain in /conf/_advanced.php ? If you set it to '.yoursite.com', all subdomains will share cookies/sessions with the main domain and captcha should work then.

Ibiblio.org hosts the site. I would have to purchase my own domain, and redirect. Good info, though. I didn't know about that.

I've checked your cookie domain, and it's ".ibiblio.org". So the captcha installed in ibiblio.org should also work on whatever.ibiblio.org

If you still have problems with captcha on subdomains, set cookie path to '/' in the same file. And change the $instance_name to force new cookies.

$cookie_path = '/';

Yahoo! Thanks much. Will share this info with the folks at ibiblio.org. I appreciate your help.

no problem ;)