Flickcurl is a library for implementing the Flickr API in C. This library supports the entire Flickr API, including functions for browsing, searching, and uploading photos and videos. It comes with a program called flickrdf that turns a photo's metadata, tags, machine tags, and places into RDF triples descriptions.
Flickr has added more real-time goodness to their photo API. Using a publish / subscribe (PubSub) system, developers can now receive real-time updates across millions of photos across Flickr friends, Flickr Commons, and by tags and geo-location using the Flickr Real-Time API.
Popular image-sharing application mlkshk now has a mlkshk API for building mlkshk-enabled applications. The service provides a social image discovery and sharing technology, with a RESTful API allowing access to a user's mlkshk account, friends, favorites, and personal image collections also known as "shakes."