The easiest way is to use the pre-built library at: https://sourceforge.net/projects/opencvlibrary/files/4.5.0/opencv-4.5.0-vc14_vc15.exe/download

Run that file to extract the contents to your hard drive (for instance, C:\temp\opencv450).

Copy the include files: Go to C:\temp\opencv450\opencv\build\include -- copy the opencv2 folder to your Visual C++ folder (for instance, C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.26.28801\include)

Copy the lib files: Go to C:\temp\opencv450\opencv\build\x64\vc15\lib -- copy the lib files to your Visual C++ folder (for instance, C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.26.28801\lib\x64)

Copy the DLL and exe files: Go to C:\temp\opencv450\opencv\build\x64\vc15\bin -- copy the dll and exe files to your C:\windows\system32 folder.

Once you have all of these files in place, you can add these to your code:

include <opencv2 opencv.hpp="">

using namespace cv;

pragma comment(lib, "opencv_world450.lib")

The easiest way is to use the pre-built library at: https://sourceforge.net/projects/opencvlibrary/files/4.5.0/opencv-4.5.0-vc14_vc15.exe/download

Run that file to extract the contents to your hard drive (for instance, C:\temp\opencv450).

Copy the include files: Go to C:\temp\opencv450\opencv\build\include -- copy the opencv2 folder to your Visual C++ folder (for instance, C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.26.28801\include)

Copy the lib files: Go to C:\temp\opencv450\opencv\build\x64\vc15\lib -- copy the lib files to your Visual C++ folder (for instance, C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.26.28801\lib\x64)

Copy the DLL and exe files: Go to C:\temp\opencv450\opencv\build\x64\vc15\bin -- copy the dll and exe files to your C:\windows\system32 folder.

Once you have all of these files in place, you can add these to your code:

#include <opencv2/opencv.hpp>
using namespace cv;
cv;
#pragma comment(lib, "opencv_world450.lib")

The easiest way is to use the pre-built library at: https://sourceforge.net/projects/opencvlibrary/files/4.5.0/opencv-4.5.0-vc14_vc15.exe/download

Run that file to extract the contents to your hard drive (for instance, C:\temp\opencv450).

Copy the include files: Go to C:\temp\opencv450\opencv\build\include -- copy the opencv2 folder to your Visual C++ folder (for instance, C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.26.28801\include)

Copy the lib files: Go to C:\temp\opencv450\opencv\build\x64\vc15\lib -- copy the lib files to your Visual C++ folder (for instance, C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.26.28801\lib\x64)

Copy the DLL and exe files: Go to C:\temp\opencv450\opencv\build\x64\vc15\bin -- copy the dll and exe files to your C:\windows\system32 folder.

Once you have all of these files in place, you can add these to your code:

#include <opencv2/opencv.hpp>
using namespace cv;
#pragma comment(lib, "opencv_world450.lib")

There is no good reason to use OpenCV 3 over 4, if you're just starting out.

The easiest way to install OpenCV is to use the pre-built library at: https://sourceforge.net/projects/opencvlibrary/files/4.5.0/opencv-4.5.0-vc14_vc15.exe/download

Run that file to extract the contents to your hard drive (for instance, C:\temp\opencv450).

Copy the include files: Go to C:\temp\opencv450\opencv\build\include -- copy the opencv2 folder to your Visual C++ folder (for instance, C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.26.28801\include)

Copy the lib files: Go to C:\temp\opencv450\opencv\build\x64\vc15\lib -- copy the lib files to your Visual C++ folder (for instance, C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.26.28801\lib\x64)

Copy the DLL and exe files: Go to C:\temp\opencv450\opencv\build\x64\vc15\bin -- copy the dll and exe files to your C:\windows\system32 folder.

Once you have all of these files in place, you can add these to your code:

#include <opencv2/opencv.hpp>
using namespace cv;
#pragma comment(lib, "opencv_world450.lib")