The Rekognition API differentiates its feature set by processing images to recognize more than just the location of faces. Rekognition's technology will analyze a given photo and present a list of scenes, each with a probability rating. Faces are not simply identified, but are also classified for age and emotion.
In related news, the FBI recently announced a $1 billion dollar budget for a new biometrics system which would include facial recognition as one of it's primary identification methods. The internet, as usual, was able to conjure up some related but unusual content in response to this story. CVDazzle is a project which has explored methods of defeating facial recognition with, of all things, fashion!
This API is hosted at Mashape, which is one of the premiere API communities. Part of Mashape's value add to the API community is auto-generation of API client libraries. There are libraries in Erlang, Objective-C, Python, Java & Ruby all ready to go. The API even has a testing console so you can dive right in!
The Rekognition site still has a few "Coming Soon!" areas, which may indicate that this is an indie project. We have more than 20 recognition APIs in the directory already.