Magickly aims to make image manipulation possible as a simple web service. The Magickly API is very easy to use, and completely open source. It requires no API key, and allows a developer to use a lot of different image manipulations on any web-accessible image. Magickly is an open source, simplified version of the Aviary Effects API, which has a contest ending next week.
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.
Of all the hundreds of tags you can see in our mashup tag cloud, the second most popular behind "mapping" is "photo". How popular? As of now there are over 200 photo-related mashups listed at ProgammableWeb -- 202 by today's count.