This invention is a device and system for monitoring a person's food consumption comprising: a wearable sensor that automatically collects data to detect probable eating events; an imaging member that is used by the person to take pictures of food wherein the person is prompted to take pictures of food when an eating event is detected by the wearable sensor; and a data analysis component that analyzes these food pictures to estimate the types and amounts of foods, ingredients, nutrients, and/or calories that are consumed by the person. In an example, the wearable sensor can be part of a smart watch or smart bracelet. In an example, the imaging member can be part of a smart phone. The integrated operation of the wearable sensor and the imaging member disclosed in this invention offers accurate measurement of food consumption with low intrusion into the person's privacy.