On a 3 ring binder, each page has a little horizontal offset. Maybe this
can be detected?

Maybe something to detect the translucency of the paper? Put a
photodetector under each side of the book. Assuming illumination is even
(a BIG assumption), the ratio of the light hitting each detector is
inversely proportional to the number of pages covering the detector. And,
you know the total number of pages, so you could calculate how many are on
each side. Seems a bit unreliable, though...

Continuing with optics... can the page sizes vary a bit, or have holes
punched in them, that would allow a go/no-go ambient light detection?

Harold



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