Update: "The app is back up and running and photos has been restored," a Facebook spokesperson told me in a statement. When I asked for details on what exactly happened, here's the answer I got back: "The app was removed in error as part of Facebook’s automated systems, which are in place to ensure apps on Facebook provide positive user experiences. We're currently working on updated tools and analytics to help developers better monitor user feedback and provide more transparency into these systems."
Users who have used KDE applications to upload photos to Facebook are finding out the social network cannot be trusted. Not only has Facebook blocked the KDE Image Plugin Interface (KIPI), but it has removed all photos previously uploaded using the KIPI, according to a bug report titled "KIPI facebook application is deleted. can't upload and previously uploaded pictures disappear" (via NetworkWorld).
The KIPI is a common plugin structure used by many KDE applications to share image plugins among graphic libraries. Many KDE applications such as Gwenview, Digikam, and KPhotoAlbum use the KIPI to upload photos to social networks such as Facebook.
Since Facebook has apparently banned the KIPI, when KDE users try to upload images using any application that leverages it, they get a "Facebook Call Failed: Invalid API key" error message. It's even more puzzling to learn that Facebook has deleted all photos that users have uploaded using these applications. My guess is that at least the second part was accidental, though of course that's not a valid excuse.
KDE developers have already filed a bug report at bugs.developers.facebook.net asking for KIPI to be restored. The bug has been marked as "RESOLVED INVALID" and they have been told to use the Disabled App Appeal form instead.
It is unknown if Facebook will be able to retrieve the photos, or what the reason behind the ban of the KIPI is. Whether you're a KDE user or not, remember to keep local backups and never assume that Facebook, or any other cloud service for that matter, can guarantee your content will be available forever.
I've reached out to Facebook for a comment on this story and will update this post once I hear back.