The workload described is event-driven, low volume, and sporadic, making serverless architecture the most cost-effective choice. AWS Lambda, when triggered by S3 event notifications, runs only when new photos are uploaded and incurs cost only for execution time.

Option C uses S3 event notifications to invoke a Lambda function whenever a new object is created. The Lambda function generates a thumbnail and uploads it to a second S3 bucket. This solution requires no servers, no scheduling, and no idle compute costs, making it extremely cost-efficient for 150 uploads per day.

Options A and B involve running long-lived compute resources that would remain idle most of the time, resulting in unnecessary cost. Option D is invalid because S3 Storage Lens is designed for storage analytics and reporting, not event-driven processing.

Therefore, C is the most cost-effective and operationally efficient solution.