The words of Genesis 1: 26 are some of the most well-known in the Old Testament: "Let us create humankind in our image and likeness." They are also some of the most debated. If you looked up the passage in serious commentaries and theology books, you would find that just about everyone and his uncle has an interpretation for what the words mean.
If we read the passage closely (Gen. 1: 26-28) and move past the English translation to the Hebrew text, the answer to what the "image" means becomes clear. Whatever the image is, it is unique to humankind and not shared with any part of the earthly creation. It is also equally and fully possessed by all humans, and it is not incrementally bestowed. When Adam and Eve had children, the text assumes the image was passed on (Gen. 5: 3). Genesis 9:6 indicates that all humans after Adam and Eve were also in God's image.
These observations are crucial, for they mean that any definition of the image that is ability-based cannot be correct. The reason is simple: the fertilized egg created at human conception has no abilities, even though it is fully human. Since the image is nowhere described as incrementally gained, the idea that the contents of the womb gain the image at some point in development is disallowed. The Bible knows nothing of humans being potentially or partially in God's image. Humanity is God's image.
But what does that mean? The answer comes from Hebrew grammar. The key phrase is that humankind was created in God's image. As is the case in English, Hebrew prepositions convey many different nuances of meaning. To illustrate in English, if I say, "Put the dishes in the sink," the preposition speaks to location. For "I broke the mirror in pieces," and "I wrote the letter in pencil," the preposition describes result and the means by which something is done. However, the phrase "I work in medicine" means that I work as a doctor, physician's assistant, nurse, or even a research scientist. The preposition denotes function or role.
So it is with the phrase in Genesis 1:26. To be created in God's image means to be created as God's image. The effect of the translation is significant. There is no sense of gaining the image in stages. To be human is to be God's image. That is a description that applies to all human life, no matter the stage of development. Ultimately, this means humans function as God's representation. We were put on earth to function in God's place - to steward his creation as though he were physically present. We may not be able to discern what God wants each person to be or do, especially those who are handicapped or whose lives are cut off prematurely. But the imaging idea informs all of biblical ethics. It also describes our Christian lives: we are to image Jesus, who is the ultimate imager of God (Rom. 8: 29; 1st Cor. 15:49; 2nd Cor. 3:18).