Rosto.io is face recognition API. It detects and predicts plenty of facial features such as landmarks, smile, glasses, age, gender, emotion. All of them using end-to-end machine learning.
Kairos - Facial recognition & mood detection API
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Google Vision AI - Cloud Vision API provides a comprehensive set of capabilities including object detection, ocr, explicit content, face, logo, and landmark detection.
API List - A collective list of APIs. Build something.
OpenCV - OpenCV is the world's biggest computer vision library
API for Product Managers - The A to Z of APIs for product managers