I’m convinced that what’s measured isn’t the accuracy of what is picked, but the delay in picking. A bot will immediately start processing the image and selecting square after square at a certain rate, while the human has that pause of “wtf?”, then multiple hesitations.

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I’ve been asked this, except it was a scooter in the picture. I correctly didn’t select any squares, but failed the test.

Scooters aren’t motorcycles!

I have a motorcycle and I still failed a motorcycle captcha.