A mirror is made of glass with metallic backing. When light travels into the mirror, it bounces back without being scattered, preserving the image in front of it. This is called "specular reflection."
If you take a photograph of a mirror, you will not see your reflection in the photograph. The film on which the photograph was captured does not have the properties of specular reflection; neither does the paper on which the image from the film negative is printed. The photograph only captures whatever was visible in the mirror at the time and at the angle at which the photograph was originally taken.
For the same reason, a mirror on television will not show you your reflection either. The film used to take a video picture of the mirror (multiple pictures in succession, like a flip book) does not have the properties of specular reflection. And, while your television screen, like many glass surfaces, may be somewhat reflective, this reflection is caused by the glass screen itself, and is not specific to the picture of the mirror showing on the screen.
If you cannot see your reflection in front of an actual mirror hanging on the wall, then you are a ghost.
"How Mirrors Work"