CloudSight - Image recognition API; send an HTTP request with an image, get a description of contents.
YOLO - Real-time object detection
Google Vision AI - Cloud Vision API provides a comprehensive set of capabilities including object detection, ocr, explicit content, face, logo, and landmark detection.
Clarifai - The World's AI
Flico - Add visual search to your Chrome browser
Imagga - Advanced image recognition technology wrapped in powerful API.