I, myself cannot see ghosts.  Either you see ghosts or you can't.  I have no idea why this is how it is and I don't plan on guessing.  My sister, mom, grandma, and my two aunts can see spirits and are psychic.  I wish I was able to see ghosts, because that would be very interesting.

When my sister Melissa was very young, probably six or seven.  The same sister that was in "The Shoulder Tap".  She had a nightmare and so she went to my mom and dad to ask them if she may sleep in their room.  They let her sleep in the crib in the corner of the room.  A little into the night and Melissa could not fall asleep.  Through the bars in the crib she noticed a women in the mirror.  She was a young and beautiful girl with long red hair.  The lady just stood there for a little while until the image morphed into an older lady.

She had black hair that was shorter than the first woman's.   Melissa was in such surprise she held still and couldn't move.  Then the woman changed into an old man that looked familiar to Melissa.  None of the three people moved in the mirror, just stood there watching Melissa.  Then it changed back into the woman with red hair, then the black haired woman, and finally the old man.  Nothing happened after that.

I think my sister is one of the most interesting people I know.  Maybe the ghosts were watching over her or they were just trying to communicate with a human, which are the usual things.  What if the ghosts and come through her dream and were now in our world.

I don't know how the image morphed to and from different people, but does that mean ghosts have powers?  They could have been different people but why would they all be seen through the mirror.  Are mirrors a way for ghosts to funnel their presence.  http://www.ighost.org/id76.html  This Link has information about mirror  superstitions.  We all know the story "Bloody Mary".

One legend tells to cover the mirrors in the house when giving birth.  Or else the deceased soul will become trapped or the person's reflection will be replaced with the Devil's reflection.  This tradition started in the early 18th century and 19th century, and is still practiced in Greece today.  This piece of information is form the link above.