Where the text says 'Let us make man in our image" suggests to me that man already existed but not in God's image. If man were a new creation at that point the text would make more sense if rendered "Let us make in our image a man". Does the Hebrew allow for this alternate rendering and interpretation? The history of man seems to predate Adam - maybe he was around just not yet made in God's image.
There is no suggestion anywhere in Scripture that any human existed before the events described in Gen 1.
However the OP is correct to sense that the phrasing in Gen 1:26 denotes a contrast with what comes before - and that contrast is with what comes immediately before in V24, 25 -
And God said, “Let the earth bring forth living creatures according to their kinds: livestock, land crawlers, and beasts of the earth according to their kinds.” And it was so. God made the beasts of the earth according to their kinds, the livestock according to their kinds, and everything that crawls upon the earth according to its kind. And God saw that it was good.
When it comes to the creation of humans we see several important distinctions from God's creation of animals as described in Gen 1:26 and Gen 2:7 -
Then God said, “Let Us make man in Our image, after Our likeness, to rule over the fish of the sea and the birds of the air, over the livestock, and over all the earth itself and every creature that crawls upon it.
Then the LORD God formed man from the dust of the ground and breathed the breath of life into his nostrils, and the man became a living being.
Thus, mankind was distinct in the following ways:
- Humans were created in "God's image"
- Humans were given the capacity to "rule" over all other creatures
- Humans were given the authority to rule the earth
- Humans were created by God personally "breathing into his nostrils the breath of life".
Thus, humans were designed to be a completely different class of life-form from all others on earth with greater responsibilities and the capacity to know and interact with God.
Note that humans possessing the "breath of life" (Gen 2:7, Job 33:4, Isa 2:22, Dan 5:23, etc.) is NOT unique to mankind as it also exists in all breathing creatures, Gen 6:17, 7:15, 22, Eccl 3:19, etc.
"for man to pre-exist not in God's image". I think this is a contradiction.
"In the beginning God created the heavens and the earth". Genesis 1:1. During creation week God starts off by creating the most fundamental aspects of the scenario into which God will put man.
As we go through creation week the things created, light, v5, plant life v12, and so on, all lead up to the last thing created, "man". What is "man"?
Man is the high point of creation. Man is the created thing which is most, of all created things, like the Creator. Hence "in His image".
"in His image" is what man is. To ask if one could have man not "in His image" is to take away the definition of what a man is.
God is holy. Psalm 99:9 "for the Lord our God is holy". Man is not holy, "If we say we have no sin the truth is not in us". 1 John 1: 8.
God is uncreated. "Even from everlasting to everlasting You are God". Psalm 90:2. Man is created.
God has all authority. "All authority in heaven and earth has been given to me". Matthew 28:18. If man has anything which looks like autonomous authority , it is authority which comes from God, who started off with all of it.
One could add many ways in which we are not like God. But because man is more like God than any other part of His creation we are still "in His image".
I think in Genesis 1:26 "man" and "in his image" cannot be separated.
While most would not read "God made man in his image" as taking an existing man, and would object to such a reading, the reason why they would object is because they have their own historical creation account in mind.
Genesis is a very cryptic book. In less than 400 hebrew words, the first two chapters cover the creation of the universe, earth, life on earth, including man. As a result, there are a huge number of different ways that people have historically filled in the gaps in order to try to understand the text, and others fill in the gaps in order to try to harmonize genesis with what is known about science at any given point in time.
There are a whole host of different approaches to reconcile the fact that we have fossils and other evidence for man that dates back to ~100,000 years ago, including evidence of the beginnings of agriculture and even burial rituals. I'll summarize some of these approaches here and let you investigate them further:
The two creation accounts. E.g. God created man and woman in Gen 1 and blessed them, but in Gen 2 there is a second account of creation in which "adam" (adam is just the word for man) is created out of dust, God breathes the breath of life into him, and "sets" him in Eden. Thus God could have taken one specific man he created and put him in Eden, leaving the rest of the men (created long before) outside Eden. This special man would be the one God choose to walk with in Eden ~6000 years ago. This view is espoused by Gerald Shroeder and this view also requires a different dating of days for the first 6 days (Shroeder argues that they are from the point of view of God in the early universe just when matter separated from energy). Schroeder also draws on some rabbinical tradition as well as scriptures that describe man who does not know God as being a "brute beast" or "beastly". Thus there are the "beast-men" and there are those who walk with God.
Cycles of destruction. This idea refers to a gap between "In the beginning" and "the earth was without form and void". In this theory, "In the beginning" happened a long time ago and many things happened between that and "the earth was without form and void". For example, the various spirits God created were tested, sent to the earth, and they created their own version of "man". Then God destroyed everything making the earth formless and void, and started creation again. In fact there may have been many cycles of creation and destruction, finally culminating in Noah, where God promised "never again" to destroy the earth with water. This view has some support in rabbinical tradition. You can read more about it here or here.
The Eden Gap. I've also heard one teacher argue that we do not know how long Adam was in the garden -- it could be millions of years, etc.
Young earth creationism. This view discounts things like radioactive dating, arguing that the universe was fundamentally different before Noah (different physical laws, perhaps). This view also argues that, for example, when God created the universe, the Sun and moon were made in their current positions and states, etc.
That all of the above are theories espoused by those who believe in the literal text of Genesis reveals just how terse and open to interpretation this text is. The bottom line is that we have to be careful in trying to reconcile scripture with science because on the one hand, it's good to have some reconcialitions, but on the other hand these are all speculations. Properly speaking, this is not hermeneutics. There are many possible ways of doing the reconciliation and they could all be wrong. Science is always changing whereas scripture is unchanging, so we shouldn't treat these reconciliations as scripture, and we should be honest as to how much of our reading of Genesis consists of us filling in the gaps rather than relying on the words themselves. It's enough to know that there are some reconciliations possible, and then there isn't much point in worrying about what the true reconciliation is. Scripture is very terse and concise. Genesis isn't a science book, it's a work of prophetic history.