When running an audit on mobile, or if I run an audit on a 4k or 5k monitor where the DPI is 2x, we get marked down on our score.

In the screengrab above, you can see that lighthouse is expecting an image of 2198x2150. You can also see that the image being served has the dimensions of 2200x1252. However, the displayed size and actual size don't correspond.

I get a 100 if testing on a standard dpi monitor.