Well my personal opinion is that such a CAPCHA could be used to mitigate counterfeit steem production as outlined in a recent blog posting of mine.

https://steemit.com/steem-network/@novacadian/where-is-the-trust-in-proof-of-brain-mining

In the context of steem mining it is my opinion that such carbon life form proof of brain upvoting should offer a greater reward than steem generated by non-proof of brain production such as via the upvotes of voting bots.