Which AWS service will meet this requirement?

Explanations:

Amazon Rekognition is a service designed for image and video analysis. It can recognize objects, scenes, and faces in videos, making it suitable for identifying employees accessing office premises through video footage.

Amazon Polly is a text-to-speech service that converts text into lifelike speech. It does not provide any capabilities for video analysis or face recognition, thus it is not relevant for identifying employees accessing the offices.

Amazon Cognito is a user identity and access management service that enables developers to manage user authentication and synchronization. It does not offer features for video analysis or employee identification, making it unsuitable for the stated requirement.

AWS Lambda is a serverless compute service that allows users to run code without provisioning servers. While it can be used in conjunction with other services, it does not provide direct functionality for video analysis or identification of employees, so it cannot meet the requirement alone.