It works on every copier ever made with an ADF as far as I can tell.
When you feed the paper on the ADF it feeds the paper across the light sensor (Light never moves)
So if there is anything at all on the glass between the light and the paper, it gets copied, and because the paper is the only thing that moves, it appears as a line from end to end of the scan.
When you lay the paper on the glass, the light moves, so any spot on that glass creates a spot, not a line, because it isn't always between the light and the paper.
And when you get really bored, you can have a lot of mindless fun by opening the lid, choosing a paper size as the original and doing a scan or copy of things that you can move on the screen/glass while the light moves.
For instance, you can roll your head as it scans to flatten your face ;-)
Or you can make a pen look like this
Not that I would condone wasting resources on ideas like that ;-)