The puzzle of Mirror Images

I ran into the puzzle of why images in the mirror are reversed left-right but not up-down. Then I found this blog, which seems to have been discontinued since 2003.

The host appears to be a grade school science teacher and was gathering puzzles and researching for the answers for his students.

So about mirror images, mirrors do not actually reverse image sideways. It is our perception of left and right that leads us ask the wrong question. He describes a simple solution:

Stand in front of a mirror facing north yourself. Raise your right arm to point east, your mirror image is also pointing east. Raise your left arm to point west, and your mirror image is pointing west. The same thing happens when you point up or down. But if you point your finger to the north (into the mirror), your image will points out of the mirror and to the south!

So the fact is, mirrors only reverse the direction of the object by the axis perpendicular to the mirror surface, just as the physical law depicts what happens to light when it hits a mirror - light traveling into a mirror travels backward (got reflected).

The host also suggests a few websites and books to read. This The Annotated Alice: The Definitive Edition seems very interesting. The books includes the original stories of Alice in Wonderland and Through the Looking Glass by Lowell Carroll and original illustrations, and very detail annotations by Martin Gardner on the historical context of the jokes and logical, topological and mathematical paradox.