You may be interested in an idea for a decentralized anonymous CAPCHA scheme, which was proposed in an old posting of mine. A link to the post is included below for your reading pleasure.
https://steemit.com/steem/@novacadian/a-decentralized-capcha-annonymous-proof-of-brain-verification
Even if only used as a tool by SMT distributors, it would be handy to be able to separate the wheat from the chaff on the blockchain.