"the image of the Trinity is in the mind primarily and mainly, in so far as the mind knows God".

"following St. Augustine, St. Thomas maintains explicitly that the image of God in man resides primo et principaliter in the knowledge and love of God, that is to say, in the participation in the knowledge and love that God has of his own mystery.  The knowledge and love of self constitutes a secondary aspect of the image of God (secundario), to the degree—and only to the degree—that the human mind that knows and loves itself is borne towards God."

     Gilles Emery, "La théologie trinitaire spéculative comme exercice spirituel suivant saint Thomas d'Aquin," Annales theologici 19, no. 1 (2005):  127-128 (99-133), citing ST I.93.8, I.93.4, and De veritate 10.7, which see!  From the latter, Resp.:

the likeness of the Trinity is clearer in mind, as knowing God, than as knowing itself. Therefore, properly speaking, the image of the Trinity is in the mind primarily and mainly, in so far as the mind knows God, and it is there in a certain manner and secondarily, in so far as the mind knows itself, especially when it considers itself in so far as it is the image of God. As a result, its consideration does not stop with itself, but goes on to God. There is no image in the consideration of temporal things, but a kind of likeness of the Trinity, which can partake more of the character of vestige.