In 1997, a digital book meant scanning it, because most books existed
only in print. To be viewed on the screen, a digitized book can be in
"image format" or "text format". The "image format" is the photograph
of the book page by page, as the digital facsimile of the print
version. The original layout is preserved, and one can leaf through the
book on the screen. The text format means scanning the book to get
image files, then converting these image files into text files using
OCR (Optical Character Recognition) software, and if possible, as a
second step, correcting the text on the screen by comparing both
versions. A good OCR software is supposed to be 99% reliable, leaving a
few errors per page. The text version of the book doesn't retain the
original layout of the book or page. It allows a full-text search in
the book, a main asset for an electronic book.