[jpalomaki]

Add heartbeat detection to verify the person is alive. [1] has one example, Google "use webcam to detect heartbeat" to find more.

[1] https://github.com/thearn/webcam-pulse-detector

[adrianN]

Add gaze tracking and have people look at a randomly moving dot.

[quickthrower2]

While entering captcha codes every 10 seconds

[byronhsu1230]

This is so useful!