In dealing with Genesis’s description of man as “image and likeness” Augustine notes that not every resemblance is an image: two ball bearings are as like as one pleases, but the one is not the image of the other. Image involves two things that are not just alike but which share a likeness arising from one being the cause of the other (like your face in a pond). Likeness, on the other hand, is a sort of equality. Image is not a reflexive relation: If you are an image of me it follows that I am not (and cannot be) an image of you; likeness is, however, correlative: If I am like you then you are like me. One difficulty is that the word “likeness” gets used of both image and likeness, but this is a problem of words: I’ll here call the non-reflective relation “image” and the correlative one “likeness”.
Now some things are persons and others are not. Among Trinitarian persons, there is only likeness and no image. Among things that exist, some are images of persons: all creation is the image of the Trinity, all artifacts are images of some person’s idea. But some things are both image and likeness: created persons.
Now it is plausible to claim that Scholasticism is very good at accounting for creatures as images but not as likenesses. Scholasticism bases any account of God on an argument about whether he exists at all, but this existence can only be established by way of a causal relation to the world. This causal relation is direct in the cosmological argument; but it is all-but-immediate in the ontological argument as well (i.e. if God alone must be, then he is the cause of all that need not be). Scholasticism thus gives us a God to which all else stands as image as opposed to likeness. If God is nothing but a cause, then created being can be nothing but an image as opposed to a likeness. But this obviously overlooks just how one can have created persons, which will in turn make interpersonal relations between God and man impossible.
Now clearly Scholasticism can never make creatures the sort of likenesses that one finds among Trinitarian persons. But it still has to clear some room for likeness as opposed to the mere likeness of an image. St. Thomas does this in three ways:
1.) By the account of man as dominus (lord) of his own action. By placing this account of the person at the beginning of the second part of the Summa, St. Thomas makes the whole second part an account of the person as dominus. He is clearly striking a note of likeness as opposed to image.
2.) By the account of charity as divine friendship. This includes the idea of man’s natural spiritual state while at the same time opening up a way to a friendship that transcends it. It is the first objection to the possibility of divine friendship that St. Thomas addresses.
3.) By his account of the beatific vision. Here St. Thomas argues that beatitude consists in one’s knowledge of God simply being God. He puts this negatively, to be sure, preferring to say that “God cannot be known by a similitude (i.e. an idea of God)”.
4.) By prayer. Thomas defines prayer as a sort of causality exercised by creatures, though it obviously includes reference to God doing something.