Utilities used to recognize captchas from dynamic.12306.cn.
Usage:
1. Download a .jpg image from https://dynamic.12306.cn/otsweb/passCodeAction.do?rand=lrand
2. Convert the image to .ppm format with ImageMagick.
3. ./recog file-name.ppm

Note, an additional file "network.data" is required for the utility "recog" to
work correctly. Program "train" can be used to generate this file. Currently
only 30%~40% of the recognitions are correct. Improve function
Captcha::segment() should be able to improve the overall correctness.