Your plugin looks great!
But how do you add new categories? I see only an option to check "Uncategorized" but nothing to add my own. I've tried this with images already in Media Library, and also while uploading new images.
Do you need to dig into the code, or is there something in the interface, like Jason Corradino's Searchable Categories (he has "+ add new category" option)?
I've logged out and in again, cleared the cache.
Used latest versions of FF and Chrome.
Latest version of wp.
Any help you can offer is appreciated!