For the car captchas, I've found actually clicking all the boxes with part of a car will always be a wrong answer (distinct from when it just makes you answer twice). Instead, you have to click on the squares that you know it thinks are cars.
This creates a twisted Turing test situation where, to prove you are a human, you have to pretend to be a machine's idea of what a human is.
This creates a twisted Turing test situation where, to prove you are a human, you have to pretend to be a machine's idea of what a human is.