UI Components / reCaptcha
In your Backendless App, go to the Marketplace -> User Interface tab and install the reCaptcha component

reCaptcha

ReCaptcha is a component of Backendless UI-Builder designer.
reCAPTCHA is a free service that protects your website from
spam and abuse.
It uses an advanced risk analysis engine and adaptive CAPTCHAs
to keep automated software from engaging in abusive activities
on your site.
In this component we use ReCaptcha v2.

UI Components / reCaptcha