In reply to Pavel Karoukin.

You can increase the complexity of a CAPTCHA, but you are correct that there is a limit to how far that can go. Eventually it will just tick the user off. The same applies to the hashcash route though as the user will eventually get sick of the length of time required for the calculation. I'm not sure what would take longer, solving a CAPTCHA or cracking a hashcash.

If you have any data on that sort of thing, I'd love to hear about it :) At the moment I'm just guessing that they'd be comparable.

I do intend to cater for your concern though, as I'm intending to have various levels of protection which will automatically ramp up as more spam arrives. If the user reports too much spam, I'll crank the protection level up a notch. Eventually there would be both a CAPTCHA as well as other various protections to stop whatever hyper aggressive spammer might be attacking your site. I am still a wee way of getting that implemented though.