That is called micropayments and doesn't need to have anything to do with blockchain.

All you need is a central clearing house service that can handle billions of 0.000001 transactions per day.

Incidentaly, I doubt the bitcoin chain could handle that...

There are off-chain solutions to handle most of the payment, and only put a summary on-chain. I think there are already micropayments in Brave or something.

At this point, why even use bitcoin, or crypto at all. Just use a crypto that is better suited to micropayments.

Proof-of-work crypto is interesting here because it is fungible with computation, so these solutions that charge computation to users are literally equivalent to crypto.

It's a solution that already has adoption, does not require everyone to sign up with a centralized service, and does not require everyone to pay money (they can pay with small amounts of computation instead) so it remains accessible to ~everyone.

Yes, sites could use a bot protection service that runs captcha breaking AIs on the viewer's browser. Said bot protection service could then break captchas for forum spammers to make real money.

I was thinking this would involve farming the mining (the energy intensive part) out to clients. That basically just means they have to do sha hashes at some difficulty. The good thing is if you do 10 hashes at difficulty 5 you'd expect one to also pattern match difficulty 6, so I expect even low-difficulty hashing will eventually result in a block mine.

Of course it isn't very secure because if the client sees a mined block they might have the technical savvy keep it. But you'd be forcing big web scrapers to run a horribly inefficient mining operation and they'd hate it. Plus you can run a blacklist of hated clients and double the difficulty for them, which is very low-cost for false positives and very high-cost for real scrapers - that isn't a result of using Bitcoin but it'd be funny.