rflickr is a Ruby implementation of the Flickr API. It includes a faithful reproduction of the published API as well as method encapsulation to provide more useful object mappings. rflickr features result caching to improve performance.
While map mashups are what have defined this genre of application, the second most popular type of web mashup here on ProgrammableWeb are photo mashups. How popular? Just this past week the number of photo-related mashups passed the 500 mark, and there are now 505 listed.
After holding off for months on an official API, popular photo sharing service Instagram has opened sign-ups for a public beta of its Instagram API. With it, developers can access the 300,000 photos uploaded daily by its more than 2 million users.