Python code using OpenCV library for face detection:

In below code,

we first load the pre-trained face detection model using cv2.CascadeClassifier Then, we load the image we want to detect faces in and convert it to grayscale.

We then use the detectMultiScale function to detect faces in the grayscale image.

Finally, we draw rectangles around the detected faces and display the image with the detected faces using

cv2.imshow 

Code for Face detection in Image

import cv2

# Load the pre-trained face detection model

face_cascade = cv2.CascadeClassifier('haarcascade_frontalface_default.xml')

# Load the image you want to detect faces in

img = cv2.imread('image.jpg')

# Convert the image to grayscale

gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

# Detect faces in the grayscale image using the face detection model

faces = face_cascade.detectMultiScale(gray, scaleFactor=1.1, minNeighbors=5, minSize=(30, 30))

# Draw rectangles around the detected faces

for (x, y, w, h) in faces:

    cv2.rectangle(img, (x, y), (x+w, y+h), (0, 255, 0), 2)

# Display the image with the detected faces

cv2.imshow('Detected Faces', img)

cv2.waitKey(0)

cv2.destroyAllWindows()

Code for face detection using Video stream

import cv2

# Load the pre-trained face detection model

face_cascade = cv2.CascadeClassifier('haarcascade_frontalface_default.xml')

# Open the video stream

cap = cv2.VideoCapture(0) # 0 for default camera, or a file path for a video file

while True:

    # Read a frame from the video stream

    ret, frame = cap.read()

    # Convert the frame to grayscale

    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

    # Detect faces in the grayscale frame using the face detection model

    faces = face_cascade.detectMultiScale(gray, scaleFactor=1.1, minNeighbors=5, minSize=(30, 30))

    # Draw rectangles around the detected faces

    for (x, y, w, h) in faces:

        cv2.rectangle(frame, (x, y), (x+w, y+h), (0, 255, 0), 2)

    # Display the frame with the detected faces

    cv2.imshow('Video Stream', frame)

    # Stop the video stream by pressing 'q'

    if cv2.waitKey(1) == ord('q'):

        break

# Release the video stream and close all windows

cap.release()

cv2.destroyAllWindows()

Code Explanation

In this code, we first load the pre-trained face detection model using cv2.CascadeClassifier. 

Then, we open a video stream using cv2.VideoCapture, with 0 for the default camera, or a file path for a video file. 

We then continuously read frames from the video stream, convert each frame to grayscale, detect faces in the grayscale frame using the detectMultiScale function, draw rectangles around the detected faces, and display the frame with the detected faces using cv2.imshow.

 Finally, we stop the video stream by pressing 'q' and release the video stream and close all windows.

Requiremnts.txt file info

The requirements.txt file is used to list the required Python packages and their versions that your Python code needs to run. Here is an example requirements.txt file that includes the packages required for the face detection code using OpenCV:

makefile
opencv-python==4.5.4.58
numpy==1.22.2

In this example, we need OpenCV and NumPy packages to be installed. The version numbers mentioned in this file are optional, but it's always a good practice to include them, so that the specific versions of the packages are installed.

You can create a requirements.txt file in the same directory where your Python code is, and run pip install -r requirements.txt to install all the required packages at once