> I'm hedging here; it feels to me that OCR-ing normal text that never left the digital realm should be 100% reliable, but I'm not a specialist in that subfield

> I'm hedging here; it feels to me that OCR-ing normal text that never left the digital realm should be 100% reliable, but I'm not a specialist in that subfield so I surely must be missing something... A string set in a given font at a given size won't always render as a fixed pattern of pixels. The font describes the curves of the letter forms and how that's rasterized depends on lots of factors such as the zoom level, exactly how the font rendering engine is implemented, whether or not anti-aliasing is turned on which is further complicated by the fact that the text can be set in any color with any other color as a background, etc. And there are a LOT of fonts. Lastly, OCR is not just about recognizing letter shapes but has to contend with how the text flows. It has to understand line-breaks, multi-column layouts, captions, pulled quotes, page-numbers, hyphenation and all the other weird shit that we make text do.