All of mankind is made in Gods own image, not just Adam. We find the pronouncement early in the Bible concerning man being created in God's image:
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.” 27 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)
This image was both on a 'spiritual' plane and on a 'natural' plane. For when the Trinity said in 'our likeness' it refers to the spiritual holy image of God, but the immediate application is that under that image man would 'rule over the fish', etc. This implication is also described in Palms 8. By the word 'natural' we mean not pertaining to spirit, love or communion with God, but pertaining to body, mind, feelings and will, as these may exists separate from God. Even an animal or the Devil has mind, emotion, will, creativity. 'Spiritual' pertains to Gods character and power whereby those natural features are made to reflect God's likeness/image.
One can see that the natural image and authority over nature was not fully lost in the fall for God said after the fall:
“Whoever sheds the blood of man, by man shall his blood be shed, for God made man in his own image. (Genesis 9:6)
However on the spiritual level, man no longer held the image of God for that image is perfect holiness and this is what man lost through sin.
1 And you were dead in the trespasses and sins 2 in which you once walked, following the course of this world, following the prince of the power of the air, the spirit that is now at work in the sons of disobedience — 3 among whom we all once lived in the passions of our flesh, carrying out the desires of the body and the mind, and were by nature children of wrath, like the rest of mankind. (Ephesians 2:1-3)
Spiritually we are 'born' with the image of our spiritual parents. Spiritually we reflect Gods image, only if we love Him, otherwise He is not our spiritual father:
Jesus said to them, “ If God were your Father, you would love me, for I came from God and I am here. I came not of my own accord, but he sent me. 43 Why do you not understand what I say? It is because you cannot bear to hear my word. 44 You are of your father the devil, and your will is to do your father 's desires. He was a murderer from the beginning, and does not stand in the truth, because there is no truth in him. When he lies, he speaks out of his own character, for he is a liar and the father of lies. (John 8:42-44)
Since we were 'all enemies of God', rather than loving God, our spiritual father was the Devil, and so was our image was reflecting evil.
For if while we were enemies we were reconciled to God by the death of his Son, much more, now that we are reconciled, shall we be saved by his life. (Romans 5:10)
Therefore, although God has a special love for mankind, even when they were His enemies, only Adam and Jesus Christ were born with His image. We do not regain that image again until being 'born again'.
As was the man of dust, so also are those who are of the dust, and as is the man of heaven, so also are those who are of heaven. 49 Just as we have borne the image of the man of dust, we shall also bear the image of the man of heaven. (1 Corinthians 15:48-49)
Man lost the spiritual image of God. Furthermore, it was not just 'marred', but entirely removed and replaced with the image of the Devil. The Devil is said to be the father of that image and kingdom, on account of his introducing sin into the human race. This has always been the faith of Luther, Calvin, etc. and included in the great doctrine of original sin.
For understanding the reformed view of original sin, refer here.
I have collected a couple quotes direct from Calvin and Luther, as one suggested I was introducing a private and new idea here. Evidently this is simply untrue.
Calvin said regarding this image:
Paul says that we are transformed into the image of God by the gospel. And, according to him, spiritual regeneration is nothing else than the restoration of the same image. ( Colossians 3:10 , and Ephesians 4:23 .) That he made this image to consist in righteousness and true holiness, is by the figure synecdochee; for though this is the chief part, it is not the whole of God's image. Therefore by this word the perfection of our whole nature is designated, as it appeared when Adam was endued with a right judgment, had affections in harmony with reason, had all his senses sound and well-regulated, and truly excelled in everything good....
But now, although some obscure lineaments of that image are found remaining in us; yet are they so vitiated and maimed, that they may truly be said to be destroyed. (Calvin's commentary on Genesis Ch 1:26-27)
Luther said it even more simply:
God announces the punishment: “On whatever day you eat from this tree, you will die by death,” as though He said: “Adam and Eve, now you are living without fear; death you have not experienced, nor have you seen it. This is My image, by which you are living, just as God lives. But if you sin, you will lose this image, and you will die.” (Luther's Works Volume 1, P63)