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In a nutshell:We offer services for detecting, recognizing, and tagging faces in any photo, through our REST's services are offered for FREE with rate limits. Whitelisting is available.You can tag and recognize users from Facebook or Twitter. Alternatively, you can train our index with your own set of users in a private namespace.Saving Facebook and Twitter tags improves recognition for you and others, while maintaining your users' privacy.We process photos from anywhere, so you can mix and match photo sources with user IDs, which could enable you to, say, recognize Facebook users in Flickr photos... ‎- courant