# What is OCR (optical character recognition)?

Source: https://epublab.com/glossary/ocr/ (updated 2026-11-03)

OCR (optical character recognition) turns images of text into characters a computer can read. Applied to a scanned PDF it adds a text layer, with recognition errors that depend on scan quality, fonts and language.

## Why it matters when you convert a PDF to EPUB

OCR is the first step for converting a scanned book to EPUB, and its errors carry into the EPUB: misread letters, lost italics, broken words at line ends. EPUBLab does not run OCR today and says so rather than produce a poor EPUB from scans.