If you are going to become an app developer, you shot stop blaming users for not learning your made up UI language, and start making your app work in their language.

I thought some apps and iOS had already responded to this workflow by doing smart things when users try to create screenshots. If they haven't yet, they should. There's no need in the common case for "screenshot" and "share main image" to have different UI entry points. Just pop up a menu asking the user that they want when they push the button.