OpenCV - OpenCV is the world's biggest computer vision library
Microsoft Computer Vision API - Extract rich information from images and analyze content with Computer Vision, an Azure Cognitive Service.
Google Vision AI - Cloud Vision API provides a comprehensive set of capabilities including object detection, ocr, explicit content, face, logo, and landmark detection.
Amazon Rekognition - Add Amazon's advanced image analysis to your applications.
Clarifai - The World's AI
CCV - CCV is a open source/cross-platform solution for blob tracking with computer vision.