Authentifications can be countered by human means, and will be even more annoying (there are already people complaining about the current system)
Yes, that's true. Haha I really do hate the authentication process that requires you to enter a set of letters and numbers that are so badly mashed together that even humans are having problem understanding. There is one type that is quite easy, the jigsaw puzzle type where you just need to put the pictures together. It is quite simple and amazingly not annoying (to me that is). But if it can be countered, than all of this is indeed meaningless.
There is another way, I notice that some forums implement this. Every first post by a new member, is not shown live immediately. It is reviewed by a moderator for that section before being approved to go live. This should stop the spam quite effectively........but will mean a lot of work for the moderators though.
I agree with this idea. Have a capcha for people under a certain rep count, when you reach it the capcha is removed.
It would definitely help, but if as Aphrodite mentioned that there are now ways to counter this, than it might not be enough to save us from the spammers.