My macbook has a vertical transparent shadow, what is the problem?

Just a week ago, my laptop suddenly has a transparent shadow showing on the screen.

When I charge my laptop the shadow will be blurrier, looks like there is no problem.

But when I remove the charger it looks worse.

(The picture is not mine. I just tried to search in the internet then saw someone having the same problem. So I borrow the his/her picture)

Anyone knows what the problem is? Any advice?