Proton, the Swiss company that develops privacy-focused online services such as email, has developed its very own CAPTCHA service to help discern between
Ask questions for a personalized answer like you get on Lemmy sign ups. A human will have to verify each request, or… you can put an AI bot to judge whether your response is botlike or human.
Require you to sign in and verify yourself with a valid identity
Require you to sign in and pay to use whatever
All options I can think of without captcha are either unscalable or require you to give up privacy.
(Not suggesting this over captcha)
All options I can think of without captcha are either unscalable or require you to give up privacy.