OCR generally does not work as you describe. The common case is for the OCR system to tag charactes in an image, so that text may be selected. More advanced systems will generate fonts from the images and replace the text with those. Either way, the text isn't reduced to a single byte.
I've read plenty of kindle books that were clearly the product of OCR. True, "cl" hasn't reduced the image of a lowercase d to a single byte, but that was the intention. Don't confuse OCR, the concept, with OCR-as-implemented-in-a-particular-way, or with a-process-that-we-called-OCR-because-OCR-is-involved-at-some-point. OCR is any system that recognizes sections of image data as matching letter shapes[1].
"Generating a font from the image and replacing the original image data with that" is a very good description of what's going on here.
[1] Or numbers, or symbols like parentheses. The basic concept is letters.
