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 Bigstock API was built for Facebook applications, print on demand services website builders, ecommerce platforms and ad creation tools. You can use the API to perform five request types: search, categories, image detail, purchase, download, and light boxes & saved images.