Web pages are protecting it selfs from spammers by system called captcha (Completely Automated Public Turing test to tell Computers and Humans Apart). It is a test that decide if page is viewed by human or bot. Today it’s notorously known. Recongizing symbols from image, counting numbers or decide which picture doesn’t match with others. Captcha shouldn’t require any knowledge from user because that would only decide how much is user educated but doesn’t determine if is huma or not.