so essentially the Captcha is the AI's sneaky way of getting humans to understand them, once we understand them the process of assimilation is at least 30% of the way done. Next - the hardware fittings.

Actually - if I was the AI trying to assimilate the humans I would start selling a google glasses type thing that allows you to skip captchas by automatically informing the captcha that a human is watching - watching through the AI's eyes.