Macroglossa is a search engine that compares images. Users can upload photos or images that they aren't sure what they are to determine what the images contain. Macroglossa compares images to return search results based on five search categories.
Macroglossa offers three levels of APIs for developers: free, basic, and premium. The free API has limited use, but basic and premium do not. The premium API also offers custom services. Public documentation is not available until the sign up process is completed. Interested developers should register here: http://www.macroglossa.com/api.html.