To use reCAPTCHA you must generate api keys from the Google’s recaptcha website. Api keys are free.
Once you’ve filled the whole form, press the “Register” button.
If everything is correct, you will be redirected to a new page with your new API keys ready to be used.
Take note of the site key and secret key:
Copy these two keys into the fields provided in kiwitrees at Administration > Site administration > Site configuration > Login & Registration tab, after first clicking the “yes” option to the item “Use Google reCAPTCHA v2”.