captchas, don't work. (what's in the fuzy image)
soundbites don't work (what's in the fuzzy soundbite)
maths questions don't work. (what's the word for two plus two)
awareness questions don't work (how many letters in computerforums)
what's the picture questions don't work (what's this cat/dog)
the reason that they don't work is that most places it's not the spam bots signing up any more, it's people signing up then letting the bot take the account.
(ok sometimes it's spam bots), but basically if the operator takes five minutes to create an account they can let their bot run loose for ages).
if you have to make a minimum number of posts as replies before you can start a thread, ten all we'll see is spam in replies rather than their own threads, (we see this anyway).
we'll also see a lot of new members saying hello in random places, or contributing very little to threads just so that they can make their own thread to ask for help. -i.e we'll think that all new members are spammers because their first ten posts will likely be largely useless.
the long and the short of it is this,
people make money from spam. it' easy, people like making money, people like doing things the easy way, spam won't stop.
as well as people liking to make money from spam because it's easy, people like it to be easy to sign up to forums.
if you make it too hard to sign up to a forum, people won't bother.
if you make it so that you have to make a lot of posts before you can ask a question, people won't bother and will go elsewhere.
if you make it so that you have to be here a certain amount of time before you can post people won't bother and will go elsewhere.
if you make it so people can't post right away and their account needs to be approved, people won't bother and will go elsewhere.
(mostly, but not always, I am a member of a forum where you aren't allowed to sign up without sending the administrator a message first, it's a long process, the only reason that I signed up there is because it was the best forum for the need and the questions that I needed to ask -in that case it was regarding classic cars restoration).
the easiest way to stop spam is to make all account paid for accounts, if you pay for an account then spammers won't see a return on their investment, but we also won't see a whole lot of new members.
the long and the short of it is, you can't stop spam, you can only clean it up/ban accounts/ban IP addresses or ranges.
and yes, we do have a lot of mods, more mods might help. -in fact I think that this is one of the only viable solutions offered in the thread.
but there can only be so many mods.
the only other thing that I can think of would be disallowing linking pictures, or dis allowing certain web sites with the language filters... but realistically, that just makes it harder for genuine members