Some of the plugins available for the spambot countermeasures are old, outdated and no longer work. The best one remaining within the core is likely the Q&A. Besides that, people have to rely on Google's Invisible reCAPTCHA. While that is good, reliance on it means having to change the core code over and over again with each revision.
I would like to propose the following:
- Get rid of GD image.
- Get rid of 3D image.
- Get rid of simple image.
- And yes, get rid of Q&A along with the reCaptcha (Google's).
phpBB should have it's own built-in Invisible reCAPTCHA plugin within the core itself. No more images, no more questions to answer, and no more reliance on a 3rd party such as Google. Let the forums determine, without any human involvement (invisible), if a human is registering or if a bot attempting to register.
I don't know how anyone would make this work, but maybe someone here will figure it out.