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.
Google Vision AI - Cloud Vision API provides a comprehensive set of capabilities including object detection, ocr, explicit content, face, logo, and landmark detection.
Kairos - Facial recognition & mood detection API
Amazon Rekognition - Add Amazon's advanced image analysis to your applications.
OpenCV - OpenCV is the world's biggest computer vision library
CloudSight - Image recognition API; send an HTTP request with an image, get a description of contents.
CompreFace - CompreFace is a free face recognition service from Exadel that can be easily integrated into any system using simple REST API.