Answers in Genesis has published an article on the meaning of the image of God by John Rendle-Short. As would be expected from this source, the article spends some time (not a lot) arguing for young-earth creationism. I'll not touch on that, as I don't consider that it matters much, in reference to the question of what God's image in humans is.
The author says that the image cannot be bodily, since God is a spirit, with no body, but he writes that:
Language and creativity,—two important parts of the image, are impossible without a body. And God the Almighty agreed to share with man dominion and authority over the animal kingdom (Genesis 1:28), an activity in which the whole man, body as well as mind, is involved. Furthermore the Son of God honored the human body by becoming flesh and dwelling among men (John 1:14) (Hebrews 2:14).
He also says that "God endues man with some of his divine attributes, . . . I shall mention six: language, creativity, love, holiness, immortality and freedom. . . . All can be summed up by saying that man, like God, has an intelligence, a mind." Rendle-Short believes that animals possess little or none of any of these. I started my study for this series believing that Rendle-Short is correct about these attributes. However, he merely asserts this. He has no direct scriptural evidence. That doesn't, of course, mean that he is wrong. The Bible is not very explicit about what the image of God is.
He closes by asserting that retarded humans possess the image of God. He doesn't really explain how severely retarded humans possess, for example, language, or, if they don't, how they may be said to still be in God's image.
Thanks for reading. I expect to continue this series.