Just to give a quick overview: The FC. MetadataExtractor reads metadata from images - either on upload, or triggered manually - and stores it in the Sharepoint columns.
As the SharePoint custom document parser interface turned out to not be available for the main image formats we had to use Event Receivers. However, those also turned out to be quite inadequate, e.g. as the ItemUpdated receiver is asynchronous and interferes with the EditForm that comes up when someone uploads a single image. Hristo Pavlov had a good suggestion on how to solve that one problem
, but it still leaves a lot of questions on how to wrap all this customization into a single feature, which is to be installed.
And beyond that there were many more individual problems attached to the different ways to upload or move images to a SharePoint library. Some of them are related to IIS and SharePoint settings in general, like for uploading large image files. I'll do a separate post on this once we're through with the release.
At this point I also want to thank our beta testers. They are still the best source of inspiration and guidance!!