在MacOS使用brew安装libjpeg，报没有权限：
$ brew install libjpeg
==> Downloading https://downloads.sf.net/project/machomebrew/Bottles/jpeg-8d.mountain_lion.bottle.1.tar.gz
Already downloaded: /Library/Caches/Homebrew/jpeg-8d.mountain_lion.bottle.1.tar.gz
==> Pouring jpeg-8d.mountain_lion.bottle.1.tar.gz
Warning: Could not link jpeg. Unlinking...
Error: The brew link step did not complete successfully
The formula built, but is not symlinked into /usr/local
You can try again using `brew link jpeg'
Error: Permission denied - /usr/local/opt/jpeg
解决方法：
在MacOS High Sierra，/usr/local目录不能再使用chown。替代方案为：
sudo chown -R $(whoami) $(brew --prefix)/*
参考：https://github.com/Homebrew/brew/issues/3228