Magickly is an image manipulation service. The hosted version of the app, magickly.heroku.com acts as the base URL, then the image URL is appended to the query string as a src=, followed by any of the supported operations.
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.