CAPTCHA is a proof of brain, anything else falls under proof of work. Going off if this as a base, I believe that a CAPTCHA system should be implemented for the steem blockchain. With posts not submitting a verified CAPTCHA (more on this later), their payout would be declined. With posts submitting the verified CAPTCHA, everything continues on as it does today. I know there is resistance to captcha systems, but one that is implemented with the results being put to use instead of discarded as simply verified or not could be of great use. This could be implemented as simply as post json_metadata with a hash of the answer. Over the course of the 7 day payout window, the same captcha will be shown to other people posting for proof of brain. If the swarm (other responders in that rolling 7 day period) decide the original answer was least likely to be selected, 0% payout. With a captcha correct answer, 100% payout. This declined payout will also apply to all curation rewards...
This will lead to encouraging people to value their upvote if used for curation rewards purposes.

Additional food for thought... The captcha could be educational, as in presenting a quick fact, then asking to verify what you just read about that fact.... Or showing a pattern, and asking to identify what of the 4 corresponding blocks of data most closely match that pattern, etc..

A lot more could be said on this idea.. but it was just an idea I had after smoking a nice big ol dab. So take it with a grain of salt ... Just brainstorming over here.

• steem
• proofofwork
• proofofbrain
• marijuana
• blockchain