Taking the eye-consciousness (cakkhu-viññána) as an example:
Nina van Gorkom Nina Van Gorkom - Abhidhamma in daily life - 13
When visible object contacts the eye-sense the eye-door-adverting-consciousness (cakkhu-dvaravajjana-citta) adverts to visible object through the eye-door. When the cakkhu-dvaravajjana-citta has fallen away it is succeeded by seeing-consciousness (cakkhu-vinnana). The function of seeing (in Pali : dassana-kicca) is performed by seeing-consciousness (cakkhu-vinnana). Seeing is vipaka: it is the result of kusala kamma or akusala kamma. We are born in order to receive the results of our deeds and therefore the current of bhavanga-cittas is interrupted and vipakacittas arise after the panca-dvaravajjana-citta.
The citta which performs the function of seeing (dassana-kicca) only sees visible object. This citta does not like or dislike, it is an ahetuka vipakacitta. Neither does it think about the object
Your question about mental image: The cakkhu-vinnana has as object a rupa.
However, it is true that later mind-door processes are taking the nimitta of the visible object which is like an exact copy.
So there are 10 vipaka cittas that arise at the sensitive matter, pasada, of the eye, ear, nose, tongue, and body. 5 are unwholesome-resultants and 5 are wholesome-resultants.
It is all happening now and at every moment. It is taken for granted yet it is so amazing. There are various conditions needed for the visible object to arise. Many conditions needed for the pasada rupa inside the eye to arise. And other conditions needed for the vipaka citta . Yet they all meet at the eyebase just for an instant before falling away.