I answer difficult questions.
Ceapa Cool channel host answered this question in the form of video material. Watching the clip below you will see the effect of the scan, but you will not find out what really happened. I will answer this question. First, I invite you to the screening.
As you can see, the effect of scanning and printing is a black spot where the light-reflecting glass was. Why did this happen? To understand this you must understand how the scanner works.
In each scanner, a light source highlights the scanned document from below. The light beam travels from one side to the other during the whole process. The image of the document placed in the device is then reflected from the angled mirror (element of the scanner), which travels at the same speed as the light beam. The reflection from this mirror is "captured" by a fixed mirror located on the other end of the device. From there, the image goes to the CCD matrix, from where it can be saved to the computer's memory.
When the document is replaced by a mirror, the image reflected from the surface below the mirror is scanned. The scanner's interior is black under the mirror. That is why all we can see is black spot and possibly fingerprints placed on the glass on which the mirror is placed.