Image annotation: Applications in Machine Learning and AI

Have you ever wondered how a camera detects objects? For instance, during the pandemic, the government in many parts of the world installed cameras at the airport that can detect people without a face mask and alarm the airport authority. Similarly, phone cameras can detect a face, puppy, and other objects and tell you what the object is. How does a camera do that? Or for that matter, how does your phone camera unlocks your phone only on seeing your face and not others.