字符切分是实现机器识别验证码的一个必要步骤。
使用PIL读入图像，进行二值化处理（Binarize），然后利用sklearn.cluster中的kmeans进行字符切分，最后用matplotlib.pyplot输出结果。
参考：http://dsp.stackexchange.com/questions/23662/k-means-for-2d-point-clustering-in-python
import numpy as np
import matplotlib.pyplot as plt
from sklearn.cluster import KMeans
from PIL import Image
##############################################################################
# Binarize image data
im = np ...
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