Google Vision AI - Cloud Vision API provides a comprehensive set of capabilities including object detection, ocr, explicit content, face, logo, and landmark detection.
CloudSight - Image recognition API; send an HTTP request with an image, get a description of contents.
Amazon Rekognition - Add Amazon's advanced image analysis to your applications.
YOLO - Real-time object detection
Kairos - Facial recognition & mood detection API
Dashmote - Dashmote bundles stock image providers to make finding stock images as easy as possible.