> I'd be surprised if every image submitted isn't going through an automated solver first with only the < 95% confidence ones being sent to a human.
Yes, that's how I'd do it too, but I don't know if they're that sophisticated yet (they'll get there though).
Even with 1 second per solve, that's only $3.60 per hour. A massive improvement over 13c, but still certainly not worth anyone in my country's time.
Additionally, it supposes that all images being solved are the kind that a human must do. Tons of CAPTCHA images being output by naive generators can be solved automatically. I'd be surprised if every image submitted isn't going through an automated solver first with only the < 95% confidence ones being sent to a human.
Actually, you could do a hybrid model where every image is auto-solved and a human can either click to confirm that the auto-solver got it right or manually type a new response. That should get your time per solve down to a second or two each.