This has been discussed before. People that create those accounts are likely using very expensive software that's really good at captcha solving. There's a high chance that there are even humans solving those captchas through a service like anti-captcha. I'll have to agree that the current captcha is not the best, but other captcha's certainly wouldn't help mutch since they can still be solved by softare or some sort of semi-automation.
I found AreYouAHuman captcha is not easy to solve by a bot like other captchas, so adding it will be useful. I also tried using bots to solve Solvemedia captcha, the difficulty increased when I did but I guess it is still easier than AreYouAHuman. I know there are human captcha-solvers but all people won't spend money for this. It will certainly helps to reduce spambots.
We should look at why those accounts actually get created. Bitcointalk is a PR 6 website, this makes it realy good for websites that want to receive backlinks around the web. Those websites that get advertised here certainly aren't looking for targeted advertising but for better website ranking. I'd suggest dissalowing newbies to link to any sorf of website through their profiles. Maybe some restrictions when posting links too. Linking to your website through a PR6 forum is a priviledge, it's so easily abused at the moment.
People that create an account should be forced wait to get some activity before they can take advantage of bitcointalk's page rank for SEO. IMO this would reduce acount creation abuse for blackhat SEO purpuses dramatially.
This is a good suggestion.
So
• Change captcha.
• 'Website URL' should be disabled for newbies.
Can anybody comment on which captcha to use and whether there should be a limit for number of registrations per IP and browser fingerprint* per period? Also on how much time should that period be.
* If it is being saved.