Why do license plates get blurred on TV and online photos?

--  Often on TV news the number plate is obscured because the family have not yet been notified by the police of a family member being killed in a car accident.

--  Police often request photos and TV footage not show the number plate of an undercover police car or of the number plate of other cars for various legal reasons.

At least for online things like Google Maps, it's to protect privacy.

Sometimes people not want it immortalized forever that their car was parked outside their mistress's house when they supposedly were out of town on a work trip, for example. 

cause they dont want to show people their license plate number

There can be more than one reason. Usually when the license plates are blurred, there is something already known about the driver; additionally, there can be other reasons such as someone thinks a suspect is driving the car and it turns out to be false. 

I don't want to say it's aliens. But it's aliens.