Ask HN: How to Pay Users of an Application?

What are the models to pay out users of an application? Let's say you wanted to pay a fraction of a cent per photo that a user uploads.

My thoughts are -

1. Have a balance and cut people a check when the amount becomes reasonable. This seems like it would run into legality issues. Are they contractors? Employees?

2. Blockchain. Each interaction is granted some credit on the blockchain. Those credits can be sold for some other purpose (hypothetically, downloading the images in the future) creating a marketplace. This one seems in a comfortable legal grey area, but you need to do blockchain dev.

3. Everything is paid. Less ad hoc and the users explicitly are contractors.

4. Profit share, kind of like how REI does it. Get some proportion of the work done back as money.

None of these seem super clear. Ideally I would just like to pay users a fraction of a cent for valuable contributions (e.g. uploading or voting to reddit). Curious if anyone is aware of something that has solved this problem, or any write ups on maintaining a large contractor work force.

Thanks!