Font's aren't quite just a collection of images. Though they almost are which makes it hard to see the boundaries.
But a computer font (as opposed to the typeface it represents) is a specialized program, ie it has logic as well as data. Specifically, kerning tables and the conditions under which to use ligatures would be lost by the approach you're proposing. But I'm not a typographer or font expert and I suspect other things also. Anyway that doesn't make it completely untenable, just not a complete & automatic process.
It is similar in concept to how recipes are handled by intellectual property law. A list of ingredients isn't protected, nor is a specific result. But a list plus instructions is. You can copy a recipe by applying a different set of instructions to the same list of ingredients, resulting in an identical dish. In this the type characters are the ingredients, but you still need to provide a set of instructions to combine them into a font. You can provide ones that create an identical result, but you can't simply copy them from the original font.