Tesseract is a free raw OCR engine originally developed by HP Labs and now maintained by Google. It works with the Leptonica Image Processing Library, and is capable of reading a variety of image formats. It can convert images to text in over 40 languages.
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Tesseract was used in these research abstracts https://dh2017.adho.org/abstracts/502/502.pdf
https://dh2018.adho.org/en/extracting-and-aligning-artist-names-in-digitized-art-historical-archives/