Legacy Lead Generation forms have the option of enabling or disabling Google reCaptcha v2 as a method of spam prevention. Newer interfaces have this built-in automatically via reCaptcha V3 and do not require configuration.
Enable Google reCaptcha v2
Under Lead Generation Settings, set Enable reCaptcha? to Yes.
Enable Google reCaptcha v2 Invisible Mode
Under Lead Generation Settings, set Enable reCaptcha? to Yes.
Under Lead Generation Settings, set Enable Invisible reCaptcha? to Yes.
Important: reCaptcha Public Key and reCaptcha Private Key settings are *not* required.