For many tasks it's cheap enough to hire captcha solvers. From that we should assume that a vastly larger number of tasks become cheap enough if someone trains automated solvers on the output of the human solvers.
It doesn't need to be perfect either in most cases - just good enough that you can drive down cost progressively by trying an automated solver first before passing it on to a human if it fails.
Ultimately you'll only stop people in those cases where the monetary value of bypassing it is very low. (EDIT: And because such solvers are reusable, you need to effectively never re-use captcha types between high-value targets and low-value targets or people will end up training solvers on high-value targets as part of paid services and they'll trickle down to lower value targets as soon as they're automated fully)
Frankly, some captcha's are getting obnoxious enough that we're getting close to the point where I'd be willing to pay for a subscription service to have people solve captchas for me just for my own personal use.
It doesn't need to be perfect either in most cases - just good enough that you can drive down cost progressively by trying an automated solver first before passing it on to a human if it fails.
Ultimately you'll only stop people in those cases where the monetary value of bypassing it is very low. (EDIT: And because such solvers are reusable, you need to effectively never re-use captcha types between high-value targets and low-value targets or people will end up training solvers on high-value targets as part of paid services and they'll trickle down to lower value targets as soon as they're automated fully)
Frankly, some captcha's are getting obnoxious enough that we're getting close to the point where I'd be willing to pay for a subscription service to have people solve captchas for me just for my own personal use.