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.
Of all the hundreds of tags you can see in our mashup tag cloud, the second most popular behind "mapping" is "photo". How popular? As of now there are over 200 photo-related mashups listed at ProgammableWeb -- 202 by today's count.
Twitter added its own photo upload feature, after years of clients adding photos via APIs such as the TwitPic API. The new feature will be slowly rolled out on Twitter.com to all users. It is also expected to be incorporated into Twitter's official apps, as well as the Twitter API, upon which Twitter builds all of its end-user services.