Hardware problem: screen
 

This is a hardware problem, not a software one. It's a problem with a non-Nokia device, which has worked excellently for several years. Hoping that a hardware expert can identify the cause and severity of the problem, I am submitting two photographs of the screen. The glass itself has no cracks whatsoever.
Best wishes. Thank you for reading.

Re: Hardware problem: screen
 

It's not a touch-screen, if this information helps.
The phone wasn't dropped, merely carried in a pocket.