The captcha seems like a terrible solution when we have someone following Penn Jillette's advice for stage magicians:

Make the secret a lot more trouble than the trick seems worth. You will be fooled by a trick if it involves more time, money and practice than you (or any other sane onlooker) would be willing to invest.

You're effectively suggesting we put up a fence (to use Moody's example) in order to show him we disapprove of what he's doing. He already knows that.