"just sharing"
I used V3 captcha with a registration form to save into sqlite db using the sqlite plugin above. Two (2) additional fields are automatically added by captcha entry, namely: 'action' and 'token' upon form submission. I just inserted 2 more fields in the sqlite db; so sql insert won't throw an exception.
In V2 captcha, upon form submission, there were no additional fields added, but I only got to make the captcha checkbox to work with the form. V2 invisible never seems to work.
Hope this info helps, and thanks for this wonderful plugin!