基于传统多标签的定长验证码识别和基于GRU+CTC的不定长验证码识别
cd ./cnn
python3 train_cnn.py
python3 eval_test_cnn.py
cd ./ctc
python3 train_ctc.py
python3 eval_test_ctc.py
https://github.com/fchollet/keras/blob/master/examples/image_ocr.py
https://github.com/ypwhs/captcha_break