Interestingly they claim that the moving images are "an H.264 MPEG-4 Video Stream that is rendered in your browser in a variety of ways" http://nucaptcha.com/fe

Interestingly they claim that the moving images are "an H.264 MPEG-4 Video Stream that is rendered in your browser in a variety of ways" http://nucaptcha.com/features/security-features http://nucaptcha.com/features/security-features but they're not--it's just an animated GIF! The one on their demo page is http://bit.ly/10vBCDf http://bit.ly/10vBCDf And Apple's production version is also an animated GIF, at least on Chrome/Linux.