“Bild” is indeed “image”. Though one also says “bilden” to mean “generate”, “create”, or “consist of”. For instance, one might us it to say that two people “bilden” a team (i.e. make up a team).
Not conclusive, but Luther uses the word Bild in his translation of Genesis 1. That it may have had or acquired the meaning pretty easily given the Bible's formative currency in those years.
It is also remarkably similar in concept to theosis - still present in Orthodox faith, but goes back to at least early Byzantine Christians and is the foundation for the concept of ascetic monks.