How to slow cars with an optical illusion?

An anamorphosis is used to show something that is only recognizable from a certain location and in a certain angle. Most of them are classically hidden inside paintings. But a city decided to use one anamorphosis to make car drivers believe that there is a child playing on the road, forcing them to slow down… where children may play and be at risk from speeding cars.

Slow down or run over the playing girl!

It would have been even better in open air. But this one is already quite nice.

Source: Geekosystem.