For anti-spam purposes, CrushNinja requires a CAPTCHA on all submission portals. This is a mandatory feature and cannot be disabled by page administrators.
The reCAPTCHA v2 is the traditional CAPTCHA solution offered by Google, which requires submitters to click on a visible checkbox and possibly do a simple challenge to prove they are human. This is the default setup used on CrushNinja.
The Invisible reCAPTCHA is Google's newer version of the reCAPTCHA. A challenge is only shown to suspicious users or bots, according to Google.
For more information, please refer to https://developers.google.com/recaptcha/docs/versions.