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Humanity of an actor is not curently technologicaly specified, and there is no common way to handle it.
Saying that an actor that it is human means that
- the actor has proven some human specific capabilities to the system
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This is the most common use case, implemented for exemple by all major free mail provider.
They use a captcha (type gimpy)to prevent massive machine registration.
Protecting user/password is also a common use case : protecting a login form with a captcha limits risks of a dictionnary attack.