A. Haar cascade algorithm is an open-source machine learning-based approach used for object detection in images, commonly used for face detection in Python. It works by training a classifier using positive and negative samples of the object of interest (in this case, faces) and then applying the classifier to new images to detect the object. The algorithm uses a series of features known as Haar features to distinguish between the object and the background. The algorithm is efficient and can detect faces in real-time video streams, making it a popular choice for face detection applications.