The Microsoft Cognitive Services Emotion API recognizes emotions expressed by one or more people in an image, and returns a face identification bounding box. It detects the following emotions: happiness, sadness, surprise, anger, fear, contempt, and disgust. For video, it returns emotions of a group of faces over a period of time. 2 paid options are available, and a free plan that limits transactions to 30,000 a month is available as well. The Emotion API uses JSON for data exchange, and API Keys for authentication.