Shutterstock Reveal - Find images online to reveal a match on Shutterstock
CloudSight - Image recognition API; send an HTTP request with an image, get a description of contents.
Pexels - Find the best free stock images about Browser Home Page. Download all photos and use them even for commercial projects.
YOLO - Real-time object detection
AllTheFreeStock - All the free stock images, videos and icons in one location
Dashmote - Dashmote bundles stock image providers to make finding stock images as easy as possible.