What service provides an on-demand workforce for tasks like recognizing objects in photographs?

Amazon Mechanical Turk provides an on-demand workforce that is ideal for tasks requiring human intelligence, such as recognizing objects in photographs. This service enables users to create Human Intelligence Tasks (HITs), where workers can perform various tasks, including image labeling and object recognition. This flexibility makes it particularly useful for machine learning projects that require annotated data for training.

While Amazon Rekognition is a powerful service for image and video analysis, it is an automated solution that uses machine learning to identify objects without human intervention. Thus, it does not directly provide a workforce for human-centric tasks. Amazon SageMaker is a comprehensive machine learning service, but it does not directly connect users to a workforce for manual tasks. Amazon Transcribe focuses solely on converting speech into text and is not relevant to visual recognition tasks. Therefore, the appropriate answer for an on-demand workforce suitable for recognizing objects in photographs is Amazon Mechanical Turk.