Instead of the user having to click the "I am not a robot" checkbox, then the submit button (or w/e), this basically binds clicking the submit button to reCAPTCHA. So whatever checks clicking "I am not a robot" would run are instead done automatically when submitting.

No idea how the additional prompts (e.g. "select the parts of the image with a street sign") are shown nicely in this "invisible" UX though.