Another solution would be to overlay an image (e.g., a cat face on top of the human face). You can find the code for that below the picture.

import cv2

# Load the video
video = cv2.VideoCapture("smile.mp4")

# Load the cat face image
cat = cv2.imread("catface.png",1)

# Get the first frame and the width and height of the video
success, frame = video.read()
width= frame.shape[1]
height = frame.shape[0]

# Load the face cascade
face_cascade = cv2.CascadeClassifier('faces.xml')

# Prepare the video object where the output video will be stored
output= cv2.VideoWriter('catoutput.avi',cv2.VideoWriter_fourcc(*'DIVX'),30,(width,height))

# Read the frames one by one, detect faces, and overlay the cat face on them
count = 0
while success:
    faces = face_cascade.detectMultiScale(frame,1.1,4)
    for (x,y,w,h) in faces:
        rscat = cv2.resize(cat,(w,h))
        place = frame[y:y+h,x:x+w]
        cv2.imwrite('rscat.jpg',place)
        blend=cv2.addWeighted(place,0,rscat,1,0)
        cv2.imwrite("fcat.jpg",blend)
        frame[y:y+h,x:x+w] = blend
    output.write(frame)
    success, frame = video.read()
    count += 1
    print(count)

output.release

Code provided by student Ali Omrani.