Hi,

 

Look,

 

In case of visible light, it has much less penetrating power if compared to x rays. Hence, it willl not be able to penetrate inside human body [ because it cannot even penetrate a bunch of papers ]. X rays are better and can penetrate human body very easily and is stopped by bones or human foetus [ once penetrating human tissue it becomes weak and is stopped by foetus tissue ].

 

So, an exact picture is obtained.