A company wants to perform automated video analysis to identify employees entering its offices. Which AWS service should it use?

Amazon Rekognition is the correct choice because it is a machine learning service that provides image and video analysis. It can identify objects, people, text, scenes, and activities, and detect inappropriate content. Specifically, for identifying employees, Rekognition's facial recognition capabilities would be used. Amazon Polly is a text-to-speech service, not relevant for video analysis. Amazon Cognito provides user identity and access management, which is unrelated to analyzing video content. AWS Lambda is a serverless compute service that runs code in response to events; while it could be used to trigger Rekognition, it doesn't perform the video analysis itself.