What about providing a telephone number, which is called automatically and where you are presented an access code? Couldn't that be a hurdle for trolls and spammers?
or SMS...
Well that'd work only for people in the US wouldn't it?
Why? I've heard there are telephones and mobile phones in europe, too. Latest rumors are, they also began using fridges and escalators. Of course only in regions with power supply.
pmsl...