I've had a 2016 5k iMac for about a year now, and have never had a screen burn-in problem. Today, I was reading a review of High Sierra, and left the computer to go continue reading it on my iPad. The brightness wasn't very bright, and the screen likely went to sleep shortly after I left (20mins is what the screen saver was set to). When I got back, I noticed a dim image on the lock screen, and I wasn't sure if it was a semi-transparent display of what was behind the lock screen. I logged in, and noticed that, yes, I had a browser page open with the High Sierra review that was clearly the same as the burn-in. But if I open up a pure grey image in google image search, I still see the shapes of the page. I never noticed this on my iMac before, and it only happened after installing High Sierra. I guess I have a few questions: 1. does your iMac have screen burn-in, or have you had an iMac with burn-in? What did you do? 2. are there steps I could take to resolve this (i.e. should i take it to an apple store? I do have AppleCare) 3. is it possible that High Sierra could have caused this, or is it more likely that it was just coincidence that I noticed it? The webpage had a grid of image snapshots showing features of High Sierra, which is why it was so noticeable. Anyway, it's been about 10 minutes, and as I'm using it the image is slowly fading, but it's definitely still there. This computer was, you know, $3.5k or so, so I'm worried about the problem getting worse or something. Thanks for reading!