Let us now see how we are to understand the expression “invisible image,” that we may in this way perceive how God is rightly called the Father of His Son; and let us, in the first place, draw our conclusions from what are customarily called images among men. That is sometimes called an image which is painted or sculptured on some material substance, such as wood or stone; and sometimes a child is called the image of his parent, when the features of the child in no respect belie their resemblance to the father. I think, therefore, that that man who was formed after the image and likeness of God may be fittingly compared to the first illustration. Respecting him, however, we shall see more precisely, God willing, when we come to expound the passage in Genesis. (Book I, Chapter 2, Part 6)

The English word "image" means a a physical likeness or representation of a person, animal, or thing, photographed, painted, sculptured, or otherwise made visible.

It is derived from the Latin imago meaning to form a mental picture, as in the imagination.

The Greek for "image" is eikon which also means a physical likeness but with a much stronger sense of incorporating the full character of the original.