The act of taking the photograph is probably not illegal. But something to the tune of "All user biometrics shall only be stored with the consent of the subjec

The act of taking the photograph is probably not illegal. But something to the tune of "All user biometrics shall only be stored with the consent of the subject." pretty much means it is illegal to do so, unless you have some sort of sign. This type of law is usually under the guise of protection of personal information, or some other flag. Though the laws vary in many countries. For the sake of argument, I'm simply saying it's not illegal to photograph someone entering your property in order to point out how "secondary" or "related" laws apply without ever explicitly being defined so.