An adequate answer to this requires (at least) 2 parts:
1) In _On the Incarnation_ Athansius argues that the image of
God in humanity was a special participation in the divine Logos,
which is both "word" and reason". Thus humanity was distinguished by
being rational ("logical", _logikos_,) and having the ability to
communicate - including being able to "hear" God. Sin (which for
A was a turning away from the path God intended for humanity rather than
an abrupt fall from perfection) means a gradual loss of these abilities,
so that humanity would fade out of existence. The Incarnation is - in
A's beautiful image - God sitting for his portrait to restore the image.
This idea has the advantage of connecting strongly with what we
understand scientifically to be the distinguishing feature of humanity,
& also makes it possible to see the ability to be God's representatives
in creation - which is what Gen.1:26-28 seems to mean by image - as a
consequence of human rationality. By itself it has the disadvantages
a. it's at best an inference from scripture, and
b. being created in the image of God refers to the
2) The distinguishing feature of Jesus' humanity is his
complete trust in and obedience to the Father. In fact, it can be
argued (e.g., Pannenberg) that it is this absolute trust & obedience
which mark him as the Son of the Father. Restoration of this image
would then be an undoing of original sin, which the Augsburg Confession
defines as being "without true fear of God and faith in God".
2) seems to me fundamental in defining the image as involving a
relationship with God, & 1) then tells us qualities humanity is to
possess because of that relationship.
I think this set of ideas can be made coherent with an
evolutionary understanding of humanity, but right now would be
speculating to get into that more deeply.
George L. Murphy