Here's a nice intro[1] that later talks about how it achieves higher accuracy using an LSTM model[2].
[0] https://github.com/tmbdev/ocropy
[1] http://www.danvk.org/2015/01/09/extracting-text-from-an-imag...
[2] http://www.danvk.org/2015/01/11/training-an-ocropus-ocr-mode...