FlickrNet is a .NET library for implementing all of the Flickr API's methods. It is designed to reduce the complexity of calling the API, especially with regards to authentication. This library can be accessed from a variety of frameworks and is written entirely in C#.
Photo editing service Aviary has added a new HTTP-based API that allows developers to pass photos through filters, effects and even basic editing operations. Aviary "soft-launched" the new Aviary Effects API last week at SXSW, when we interviewed Aviary's Michael Galpert (video below). The new service could be used to create photo-sharing services like Instagram, CMS plugins to aid workflow or within social applications to create a standard look to all avatars.