基于级联分类器的人脸检测示例"face_detection.cpp"：

#include <opencv2/opencv.hpp>

int main(int argc,char *argv[])
{
    // load face classifier
    cv::CascadeClassifier faceCascade;
    faceCascade.load(argv[3]);

    cv::Mat image = cv::imread(argv[1]);

    std::vector<cv::Rect> faces;
	faceCascade.detectMultiScale(image, faces, 1.1, 3, 0, cv::Size(30, 30));

	for (size_t i = 0; i < faces.size(); i++)
	{
		cv::rectangle(image, faces[i], cv::Scalar(0, 255, 0), 2);
	}

	cv::imwrite(argv[2], image);

    return 0;
}

CMakeLists.txt：

cmake_minimum_required(VERSION 3.16.3)
project(OpenCV_face_detection_demo VERSION 1.0.0 LANGUAGES CXX)

find_package(OpenCV REQUIRED)
include_directories(${OpenCV_INCLUDE_DIRS}) # Not needed for CMake >= 2.8.11

# several variables will be set by OpenCVConfig.cmake
message(STATUS "OpenCV library status:")
message(STATUS "    config: ${OpenCV_DIR}")
message(STATUS "    version: ${OpenCV_VERSION}")
message(STATUS "    libraries: ${OpenCV_LIBS}")
message(STATUS "    include path: ${OpenCV_INCLUDE_DIRS}")
message(STATUS "    install path: ${OpenCV_INSTALL_PATH}")

add_executable(OpenCV_demo.out ${CMAKE_CURRENT_SOURCE_DIR}/src/face_detection.cpp)
target_link_libraries(OpenCV_demo.out ${OpenCV_LIBS})  # or "OpenCV_LIBRARIES"

编译执行：

mkdir build && cd build
cmake ..
make
./OpenCV_demo.out ./lean.jpg ./lean_face.jpg haarcascade_frontalface_alt.xml