Unsplash - Unsplash is a website with high-quality free HD images. It has a catalog of more than three hundred thousand striking images that are neatly organized with tags. Read more about Unsplash.
CloudSight - Image recognition API; send an HTTP request with an image, get a description of contents.
AllTheFreeStock - All the free stock images, videos and icons in one location
YOLO - Real-time object detection
Pexels - Find the best free stock images about Browser Home Page. Download all photos and use them even for commercial projects.
Dashmote - Dashmote bundles stock image providers to make finding stock images as easy as possible.