方法1

编译时出现下列错误：

undefined reference to 'cv::imread(cv::String const&, int)'
undefined reference to 'cv::String::deallocate()'
undefined reference to 'cv::imread(cv::String const&, int)'
undefined reference to 'cv::String::deallocate()'
undefined reference to 'cv::String::allocate(unsigned long)'
undefined reference to 'cv::String::allocate(unsigned long)'
undefined reference to 'cv::String::deallocate()'
undefined reference to 'cv::String::deallocate()'

解决方法：在CMakeLists.txt（目录opencv3.4.2\opencv\sources）加入安装OpenCV的版本号：
将
find_package( OpenCV REQUIRED )
更改为
find_package( OpenCV 3 REQUIRED ) 。

方法2

修改QT项目内的.pro文件中的静态库（libopencv_*.dll.a）的链接路径，由相对路径改为绝对路径，路径中不能有中文以及特殊字符。可以选择如下方式一次性添加所有的库：

LIBS += -L E:\QTProgram\testOpencv342\lib\libopencv_*.dll.a

也可以逐个添加

LIBS += E:\QTProgram\testOpencv342\lib\libopencv_calib3d342.dll.a