yes, it's definitely a good idea to emit a JSON array even when just one image is read. This ensures the programmer can use the same logic (array iteration) to process a single or multifile-output.

About the boolean values: here we are in an old dilemma - do we want the value to be "queryable" in a database (then boolean values/enumerated constants would be a better option) or "presentable" to an enduser (this means to provide meaningful translations of the values).

I see this problem in a bigger context (also with the recent translation efforts). I think it's to early to definitely decide on it. For now, just implement JSON support in your way... I'm sure sooner or later there will be suggestions to refine it with additional export options.