Bayesian Filtering is a good solution for email - but its just not too handy to try on anything but a server level.
Sure you could train /ignore commands with a client side script, but still it takes a toll on teh server's throughput.

The failing of the +v method for spamming is that it still lets bots get nicknames and send privmsg spam; but at least we know that the basic method works. :P

Decoding an image and OCRing it is leaning towards specialisation too much for most HTTP web bots, whiule it could be done; the resouces needed to do it are... extensive to say the least.

I don't think that forcing users to view an image on connect to pass a turing test is effective for a client like mirc. *sigh*

Lets see have I missed any posts?