Possible Clues:

• Modern test of humanity
• Online "humanity" test
• 'I'm not a robot' test
• Letters you see to be typed, for example S-K-I-P T-E-A
• Challenge to prove you're human
• Modern screen test
• Turing test to tell machines and humans apart
• Spell check?
• Test for screening out bots
• Weapon against automated enemies