New ask Hacker News story: Ask HN: What is the best way to confirm that an AI is not a human being?

Ask HN: What is the best way to confirm that an AI is not a human being?
3 by schappim | 5 comments on Hacker News.
I'm creating a service for Artificial Intelligences (AIs) and need to prevent human signups. What's the best way to identify if an intelligence is artificial?