I've just activated the mathcaptcha addon in order to prevent automated registrations.

The mathcaptcha addon is not yet bundled with the Friendica release, but you can find it here: https://git.friendi.ca/tobias/mathcaptcha

So, if you experience problems, please drop me a mail under my Friendica address... or webmaster or postmaster or whatever... I'm not that hard to find on the Internet... ;)