How does the "Windows XP pirated edition" wallpaper reveal more details, when I draw a selection rectangle over it? See for yourself:
Before:
After:
Unfortunately, I only own a Mac so I can't tell for sure whether this effect is Mac-specific or not. Opening the image in Preview looks like the top picture.
The box is lightening the background inside of it (compare the black in and out of the box).
The shiny bit is always there, but it's just too similar to the background to see. Lightening things brings back the detail of the shiny that was probably obscured by the computer monitor and its calibration.
To test, try opening the image in a photo editor and increasing the Brightness or Exposure.
