# What happens with a scanned PDF

Source: https://epubcc.com/cases/scanned-pdf/ (updated 2026-11-04)

EpubCC does not do OCR yet. A scanned page with no text layer is left out with a warning; a scan that already carries an OCR layer is converted from that hidden text, with its errors. On an 1867 Alice scan our 8-gram recall is 0.513, below PDFium (0.651) and pdf_oxide (0.632).

Problem: A photographed 1867 book: every page is an image, with an invisible OCR text layer added by the scanning project. The OCR has misread words, split lines and put illustration captions in the middle of the text.

- Limitation: No OCR: pages that are only an image are left out of the EPUB, and the report lists them (14 here: covers, plates and library pages).
- Limitation: OCR errors in the PDF are copied, not corrected: «MAKMALADE» for MARMALADE, «I Ve» for I've.
- Limitation: Words the OCR placed on a slightly different baseline become superscripts, and chapter openings with drop caps produce false headings (132 «chapters» instead of 12).
- Limitation: PDFium (0.651), pdf_oxide (0.632) and OpenDataLoader (0.625) recover more of this OCR text than our engine (0.513).
- Limitation: The reference is a different edition (Project Gutenberg, 1865): good for recall, not for exact precision.