I don't believe in the literal meaning, that God has a corporeal form and we represent his physical image. I'm pretty sure that most if not all ancient philosophers believed this. At the very least, St. Augustine seemed to. In any case, the idea "we are made in his image" implies that we are not God, only similar in aspects. We are a lesser being given some aspects of God, or a god. Evil, by some's definition, is the absence of good, rather than being an entity itself. Therefore, our "inherent evil" would be a result from parts of us that are not good, or godlike. Or if you want to look at it this way, part of life is growth and understanding. Since doing that is "good," and we are absent of that in birth, then we are absent of that good in the beginning. Being absent of good is evil, thus making us by that definition inherently evil in birth.