I have to assume that this is exactly what this would be for. 9gag or some similar site stealing content en masse from elsewhere and wanting to remove any sort of identifying marks.

Also my first assumption. When I read that task, being a retired professional photographer who made a living for 15 years with camera, my blood pressure rose.

:D

Captcha solving is expensive for spammers.

I can assure you it is not. It's about $0.001 per solved captcha with 97% accuracy rate and refunds on failed ones, from the service provider I know of.

I've even written one, it's not complicated and not expensive.

It is still the same rate. 2.2 ish for new recaptcha, too.

Yeah I was able to beat that "Robot check" checkbox by Google using some fuzzy bezier curves and random mouse movements/scrolling to simulate a real user's behavior.

Unfortunately Google has some other metrics to detect bots (such as no cookies showing they've seen you before, etc), so it wasn't 100% reliable.

you don't need 100% reliability, that's the good side :)

Can confirm, it was very cheap 5+ years ago when I was in the business of needing them solved en masse. I doubt it's gotten more expensive.

are you sure? What's your source?