Imago Dei

Human beings, we read in Genesis 1, are created in God’s image and likeness. Throughout the centuries theologians have struggled with these terms, trying to ascertain their precise meaning. Some have concluded that they refer to the fact that humans, unlike other creatures, have the ability to reason and so to communicate with God. Others believe that they point to the human ability to establish relationships, and still others that they must be interpreted in a functional sense, referring to the fact that human beings were appointed as God’s vice-regents with the specific task of ruling the rest of creation.
- From Reformed academic

Then God said, "Let us make man in our image, after our likeness. And let them have dominion over the fish of the sea and over the birds of the heavens and over the livestock and over all the earth and over every creeping thing that creeps on the earth." So God created man in his own image, in the image of God he created him; male and female he created them.
Genesis 1:26-27

He is the image of the invisible God, the firstborn of all creation.
Colossians 1:15

The concept of man as the image or likeness of God tells us that man as he was created was to mirror [i.e. to make visible the Invisible] and to represent God [i.e. to act as God, under God and for God's creation].
Anthony A. Hoekema Created in God's Image, pg. 67

We must learn to know what the image of God is by looking at Jesus Christ. What must therefore be at the center of the image of God is not characteristics like the ability to reason or the ability to make decisions...but rather that which was central in the life of Christ: love for God and love for man.
Anthony A. Hoekema Created in God's Image, pg. 22