Hi, I'm David an independent advisor and user just like you. I'll try and help you solve this problem.
That looks like a problem with the actual lcd panel (ie. the physical screen). I assume those blacks marks stay exactly the same no matter what is on the screen (IE. while loading Windows, logging in, on desktop, etc)?
The answer would be to have the screen replaced - this is a simple job for a repair shop to do for most laptops. Doesn't usually cost too much either.
Regards,
David