http://www.sohu.com/a/323153211_823210
https://www.cnblogs.com/tongye/p/10734342.html
https://github.com/tesseract-ocr/tesseract
https://blog.csdn.net/u012234115/article/details/80552179
https://blog.csdn.net/sylsjane/article/details/83751297
https://blog.csdn.net/IDMer/article/details/45560341