Does my screen have burn in or is it something else?

My Samsung Galaxy S7 appears to have burn in, just like in this image: (Not my phone. Image from Android Authority ) The difference is that no matter how hard I look, I can't see any icons or any other irregularities in the white bar. It appears to be perfectly uniform. It's exactly where my notification bar is in portrait mode, but I use my phone in landscape mode a lot too, and there is no colour/brightness difference at the side. Also, the white bar is _brighter_ than the remainder of the screen: I would expect burn in to make it duller. What is causing this? 1. burn in 2. hardware 3. software