Playback Mirror
Potential location: Swing box
Like a mirror
Projects the shot you just took, and superimposes that on the image of someone hitting the ideal tennis shot.

This turns swing box into almost a batting cage -
For the overlay (hitting the ball to the camera) requires that the ball comes from the same place every time and requires the player to stand in a specific place.
 

 This can be better than dartfish - showing you from the front - like a mirror.

This can be better than dartfish - showing you from the front - like a mirror.

If the camera is to the side (left or right of the student):

 Sequence of a race horse galloping. Photos taken by Eadweard Muybridge, first published in 1887 at Philadelphia

Sequence of a race horse galloping. Photos taken by Eadweard Muybridge, first published in 1887 at Philadelphia

 Dartfish

Dartfish

 Dartfish

Dartfish

A la Dartfish
http://www.dartfish.tv/