Today’s invention is stereo books, for secure reading.
A bookmark, shown in grey, can be cut to comfortably fit the brow of a user. This is placed between two pages (as shown).
Opposite pages each carry one of a stereo pair of images. The bookmark enables these images to be more easily ‘fused’ by the user so as to generate a 3-D image.
The book could be full of such images. It might also be used as a simple way to allow secure reading of confidential text eg on a plane or train, since each page could be composed of an illegible set of letter components.