Linux下OpenCV，出现错误：
ASSERT false in file qasciikey.cpp, line 501
可能是OpenCV的版本有问题，需要重新安装一下：
pip install -i https://pypi.tuna.tsinghua.edu.cn/simple opencv-python
pip install -i https://pypi.tuna.tsinghua.edu.cn/simple opencv-contrib-python
如果出现提示：
Could not install packages due to an EnvironmentError: [Errno 13] Permission denied: '/anaconda3/lib/python3.7/site-packages/opencv_contrib_python-4.1.0.25.dist-info'
Consider using the --user option or check the permissions.
表示需要使用--user：
pip install --user -i https://pypi.tuna.tsinghua.edu.cn/simple opencv-contrib-python
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