问题：

直接pip install opencv-python报错信息如下 :

Failed to build opencv-python
ERROR: Could not build wheels for opencv-python, which is required to install pyproject.toml-based projects

我这个虚拟环境是python3.6的版本,pip install opencv-python是安装最新版本，并不适配python3.6，所以要安装对应的版本，比如4.3.0.38

解决：

pip install opencv-python==4.3.0.38

 这就OK了

也可以加个其他源，比如清华源：

pip install opencv-python==4.3.0.38 -i https://pypi.tuna.tsinghua.edu.cn/simple