There's an assumption (or was once)
that because the camera is a mechanical method of creating an 
image of the world, the image it creates is
the truth. It confirms perspective: an image being of a single point in time
seen from a single point in space; as the most realistic view of reality.
Scanners and photocopiers are also
methods of mechanically creating images, but they do not use perspective, nor are they an image of single
point in time, as the scanner's bar takes a while to travel the length of the
scanner.
There are a few things that
scanners cameras have in common that manual methods of depiction had not noticed before photography-
focal length, and the lines and spots of light known as lens-flare that you get
when pointing a camera at a light. Scanner lens flare looks very deferent, though.
The problem with scanners as a
photography tool, however, is the light that is attached to the scanning arm.
This is the equivalent of
having a flash attached to you camera that you are incapable of turning off,
making setting up your own
lighting for a scan impossible.