OpenCV, opencv_contrib，Python の opencv-python パッケージのインストール（Ubuntu 上）

sudo apt -y update
sudo apt -yV upgrade
sudo /sbin/shutdown -r now

sudo apt -y update
sudo apt -y install libopencv-dev libopencv-core-dev python3-opencv libopencv-contrib-dev opencv-data

curl -L https://github.com/opencv/opencv/blob/master/samples/data/fruits.jpg?raw=true -o fruits.jpg

#include<opencv2/opencv.hpp>

int main (int argc, char *argv[])
{
  cv::Mat bgr = cv::imread("fruits.jpg");
  cv::imshow("", bgr);
  cv::waitKey(0);
  cv::destroyAllWindows();

  return 0;
}

g++ -I/usr/include/opencv4 -o a.out a.cpp -lopencv_core -lopencv_highgui -lopencv_imgcodecs
./a.out

sudo apt -y update
sudo apt -y install python-is-python3 python3-dev python-dev-is-python3 python3-pip python3-setuptools python3-venv build-essential

import cv2
bgr = cv2.imread('fruits.jpg')
cv2.imshow("", bgr)
cv2.waitKey(0)
cv2.destroyAllWindows()