The Gravatar Ruby SDK by Gravatar can generate image URLs and communicate with the XML-RPC API. The SDK aims to be useful to implement avatar photos in an application. Resources include installation, usage, and configuration.
Why did Pinterest remove its API documentation earlier this year? Well, apparently there is no rush to release an already developed API to the public yet. In fact, it may not be released for a while as Pinterest wants to avoid re-tweeting the #mistakes Twitter made in its infancy.
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.