You can see in this screenshot MarsEdit's initial Flickr authorization pane, the first step in granting access to MarsEdit to both post and access your photos stored on Flickr. In the other two tabs, namely "Upload" and "Catalog" are interfaces that allow you to conveniently upload photos and images to your existing blog, provided they support file uploads. The problem is that the former "upload" process leaves MarsEdit somewhat blind in that, unless you upload an image with MarsEdit, it will have no knowledge of other photos that you might have previously uploaded, making the utility of that feature much less generally useful.

This plugin would aim to replicate the Flickr API within a single WordPress instance such that tools like this, if they support XRDS-Simple discovery, could provide a rich uploading, manipulation and access experience similar to what you get when you use a native Flickr uploading tool. Ultimately this service API could also be exposed to third parties and authorized using the OAuth protocol and OAuth tokens.

The benefit and purpose of mirroring the Flickr API is to, on the one hand, reduce the need to learn a new photo sharing service API and on the other, to hopefully leverage the large number of existing tools and web services that have already implemented the Flickr API and might be willing to change their service to support more than just Flickr as the single storage and retrieval endpoint.

Two projects exist that might be useful to start (though are primarily implementations of the "read" methods for the Flickr API):

• phpFlickr
• Addicted to Flickr