Why scan mirror — black spot?

If you to scan a mirror, we get the black spot
mirror_scanned.jpg

A scanner arranged on the principle
Scaning_Technology.PNG
October 8th 19 at 00:47
2 answers
October 8th 19 at 00:49
Solution
Because paper reflects light in all directions, as from a mirror in one, which does not "see" the sensor.
And that the light source radiates only in one direction? - jett.Borer38 commented on October 8th 19 at 00:52
October 8th 19 at 00:51
By the way, it's not black. Black will be when you mirror wash.

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