Back on topic, I think the only possible way to do a "Proof of Human" coin is by using something that is unique to each human, but verifiable to be a human. In other words, you can't just use a person's name and address, or social security number, because those could be faked and a headless decentralized system would be none the wiser. The advantage to using such a system is that distribution and verification is incredibly simple: Simply give each person an equal amount of coins, and let the currency inflate slowly along with the birthrate (since babies would also be given coins upon birth, unspendable until they turn 18 or something).
So, you have to have something that cannot be machine-faked, which is DNA. But it can still be electronically faked, in that you could create an artificial DNA sequence. How could the headless system verify that such a human actually exists? With images!
To receive your initial distribution of coins, you have to give up a sample of DNA. A scratch of skin cells off the back of your hand, perhaps. Then, in order to spend your coins, you must verify that you are, in fact, the owner of said DNA. Fingerprints are unique - perhaps a machine could match your fingerprints to your DNA. Definitely not now, but 10, 20 years in the future? Maybe.
But then, if a machine can match your DNA to your fingerprint, what is stopping someone else from grabbing a sample of your DNA, mapping it, and then figuring out what your fingerprints should look like? And subsequently making a model of those fingerprints to be used on whatever is scanning the fingerprints, of course.
The problem with humans is, there's no one-way function for us. If you know the fingerprints, you can discover the DNA. If you know the DNA, you can discover the fingerprints. Etc. There is no human hash function.
Two separate issues.
1) Algorithms that require human input are going to be very important. Artificial intelligence algorithms require constant human input. Not talking of course of the coins that claim ai to get investors, but of an actual ai coin in the future.
2) Distribution based on x per person rather than x per computing power a person owns etc. Coins that go in that direction also will have advantages in a lot of the world. Look at India's aadhar system that will include biometerics
https://uidai.gov.in/