Checkbox is V2 and will still ask images checking if Google is not sure if you are a human.
Invisible does not have the checkbox and will still ask images checking if Google is not sure if you are a human.
But normally V2 and Invisible do not ask for image checking, you are most likely triggering Google to question your robot/human status because you are testing their ReCAPTCHA.
Make sure you only have one reCAPTCHA installed, or if you have more than one, make sure they are the same version, V2 OR Invisible.
Thanks