The correct service for this use case is Amazon Macie, which leverages machine learning to automatically discover, classify, and protect sensitive data stored in object storage. It is designed to provide continuous protection, enabling compliance with privacy regulations. This contrasts with other services mentioned: Amazon GuardDuty does not classify or provide protection for data in storage but instead focuses on threat detection and monitoring. Amazon Cognito is not designed for data monitoring but for managing identities and access. AWS Shield protects against DDoS attacks and is not tailored for sensitive data classification or protection in storage services.