Rob Church:
Another option is MathCaptcha, which sits between the text-based sum
captcha and FancyCaptcha in terms of "crackability", I suspect...
We aren't likely to ever start incorporating extensions into the core
code, ...
Another issue about having a "standard" MediaWiki captcha is that people
are likely to put significant effort into bypassing it, thus rendering
it useless -- unless it's *super*-secure, which today seems to mean
making the site less accessible to people with visual impairments, etc.
If we all pick one or two captcha schemes and hack them according to our
personal tastes, we'd probably get decent security for less cost to our
users.
Ian