In reply to Ryan Hellyer.

But you can't change complexity of the captcha with simple number adjustment. (at least with reCaptcha). There were some plugins which allowed to change level of distortion, but there is limit too.

With hashcash you have flexibility - if you get tons of spam non stop - you increase value of complexity. So for example if spammer posts 1000 messages, and with complexity of 0.01 it takes on good machine and browser average 5 seconds, it takes him 5000 seconds to post it.

Now you increase it to 0.02 and now it twice as long while regular user have to wait 10 seconds instead of 5. (and i am working on idea where calculation will be happening in background, so user really will not be waiting anything in most cases)