1. A method, comprising: electronically scanning an image-based document to determine positions of word images in the image-based document; extracting the word images from the image-based document; grouping a subset of the word images into a word cluster based on a similarity of the word images; generating a character-encoded transcription for the word cluster based on the word images in the word cluster; and adding the character-encoded transcription to a text-based electronic document at locations corresponding to the positions of the word images in the image-based document.