I would also like to add my voice to this request. What I think would be the nicest/most flexible way to do this is to let the user pick one or more metadata fields (maybe up to 3) that they want to expose for editing (this would be a global setting, not image-by-image). Then, perhaps using one of the mechanisms above, the edit fields would appear and you could make your changes. This would be super handy when I’m traveling and want to add some notes to an image while it’s all fresh in my mind.