Let users insert their own images they can view as Emoji instead of their defaults

I'm trying to write an application which would allow users to switch their default Emoji images associated with the appropriate Unicode character, with a picture of their choosing (any image of their choosing, including a new image from the camera).

I'm quite certain that this Application will need Root permission, as similar applications (such as Emoji Switcher) need that.

My question is, where are Emoji stored in an Android phone? And is it possible to encode something like a .jpg into the format that Emoji are saved in?