Originally Posted by DeathSlam

I suspect that at this stage they are still trailing it so they are using AB testing and monitoring the results (like how many people abandon the login, how log it takes to login etc). So it may be random.
There seem to be different options like just clicking "I am a human" or sometimes clicking on a picture of a monkey, so I think the final form has not been finalised. I have seen this in yahoo recently as well.