Segment region, line, recognize with tesserocr

Required ubuntu packages:

• Tesseract headers (libtesseract-dev)
• Some tesseract language models (tesseract-ocr-{eng,deu,frk,...} or script models (tesseract-ocr-script-{latn,frak,...})
• Leptonica headers (libleptonica-dev)

pip install -r requirements
pip install .

If tesserocr fails to compile with an error::

$PREFIX/include/tesseract/unicharset.h:241:10: error: ‘string’ does not name a type; did you mean ‘stdin’?
       static string CleanupString(const char* utf8_str) {
              ^~~~~~
              stdin

This is due to some inconsistencies in the installed tesseract C headers (fix expected for next Ubuntu upgrade, already fixed for Debian). Replace string with std::string in $PREFIX/include/tesseract/unicharset.h:265:5: and $PREFIX/include/tesseract/unichar.h:164:10: ff.

If tesserocr fails with an error about LSTM/CUBE, you have a mismatch between tesseract header/data/pkg-config versions. apt policy libtesseract-dev lists the apt-installable versions, keep it consistent. Make sure there are no spurious pkg-config artifacts, e.g. in /usr/local/lib/pkgconfig/tesseract.pc. The same goes for language models.