I don't think the self.optimizations hash set should belong in the Image struct as Image struct is more of a low level interface and ImageOptimization is a high level enum as it's UI facing (designed to be called by the UI).

It would make more sense for it to sit in ImageHandler, that struct is a high level interface to the Image struct. It's designed to be called by the UI.

More changes to the Image struct may be done in this issue too.