CAPTCHA from http://download.csdn.net/
finished.
Programing Language: C++
Library: opencv2 + libboost
split the letter averagely, and use KNN to recognize every letter.
cd downloader
python downloader.py
cd ./spliter && cmake . && make
./spliter
You can check the result at ./recognizer/dataset
cd ./recognizer && cmake . && make
./recognizer test1.png
./recognizer test2.png
./recognizer test3.png
./recognizer test4.png