The short answer is that all creatures, even the humblest, bear a certain resemblance to their Creator. However, of all the creatures we are familiar with on earth, only man can be said to be “in God’s own image” (to paraphrase Gen. 1:27).

I will now explain in greater detail.

All creatures bear a resemblance to their Creator

The first thing to keep in mind is that all creatures bear a certain similarity to their Creator. This occurs, because, as St. Thomas Aquinas says, causes always produce effects that are similar to themselves. For example, when the stove causes the water to boil, the stove communicates its own heat to the water. When a mother and father beget a child, they communicate their human nature to that child.*

In a similar way, when God creates any creature whatsoever, even something humble like a stone, at the very least He communicates His being to that creature. (See Catechism of the Catholic Church [CCC] 301.) Because they receive their being from there Creator, all creatures all have a share in the properties of the Creator’s own being: for example, goodness, truth (i.e., intelligibility), and beauty.

(These ideas are probably best expressed in St. Thomas Aquinas’ Summa theologiae [S.Th.]. See, for instance, Ia. q. 44, especially article 1. Regarding the similarity of the effect to the cause, see Summa contra gentiles [SCG], Book 2, Ch. 36, No. 5. Regarding goodness and the properties of being, see Ia. q. 5, especially article 1.)

Animals (nephesh) have sensitive life in common with us

Different creatures, however, participate in the perfections of their Creator in differing degrees. The humblest creatures, such as stones, participate merely in God’s being.

Living creatures participate not only in His being, but also in His life. Animals in particular enjoy a a degree of participation in God’s life that allows them to acquire sensitive knowledge (the kind of knowledge that only requires material senses) and sensitive appetite (the natural attraction that animals feel to things that benefit them). (For a fuller overview of what “life” is, and its different levels, see S.Th. q. 18, a. 3.)

The Bible calls creatures with this kind of life as nephesh (sometimes translated “soul” but better rendered as “living being”). For example, the animals referred to in Genesis 2:19 are nephesh:

Now out of the ground the LORD God had formed every beast of the field and every bird of the heavens and brought them to the man to see what he would call them. And whatever the man called every living creature (nephesh), that was its name (ESV).

Being nephesh is something that man has in common with the other animals:

then the LORD God formed the man of dust from the ground and breathed into his nostrils the breath of life, and the man became a living creature (lenephesh) (Gen 2:7).

Possessing animal (sensitive) life is clearly a more perfect participation in the life of God than that found in plants or nonliving creatures. Genesis does not, however, say that animals are created “in God’s own image;” that privilige is reserved to man alone, as it requires an even more perfect participation in that life.

What it means to be “in God’s own image”: having rational life (ruach)

Man, in addition to animal life (to being nephesh), possesses rational life. As a consequence, he is capable of truly rational knowledge and true acts of love.

Genesis shows the uniqueness of this kind of life through the image of breath or wind (neshamah or ruach):

then the LORD God formed the man of dust from the ground and breathed into his nostrils the breath [the word used derives from neshamah] of life, and the man became a living creature. (Gen. 2:7).

Breath and wind are, however, also images for spirit (that is, for beings that are by nature not dependent on matter for their existence, like men, angels, and God):

And the Spirit [the word is ruach, which can mean “spirit” or “wind”] of God was hovering over the face of the waters (Gen 1:2).

It is only the creatures with rational (that is, spiritual) life that can be said to be “in God’s own image.” That is why Gen. 1:26 only attributes this privilege to man:

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.”

Likewise, in the following verse:

So God created man [understood in the inclusive sense of “mankind”] in his own image, in the image of God he created him; male and female he created them (Gen. 1:27).

(As a side note, since men and women participate equally in rational life, it follows that we are both equally in the image of God.)

It should be noted that it is not exactly the human intellect alone that causes man to be in the image of God. Rather, we are in His image because we possess rational life and everything that such a life entails. Creatures that possess rational life also possess animal and vegetative life, as well as being. Having rational life simply means that we participate in God’s Divine Life to a much greater degree than sub-human creatures.

As the Catechism puts it,

Endowed with “a spiritual and immortal” soul, the human person is “the only creature on earth that God has willed for its own sake.” From his conception, he is destined for eternal beatitude (No. 1703; the quotations are from Gaudium et spes 14 § 2 and 24 § 3.).

Man is said to be in God’s “image,” because he is capable of actions that make him strikingly similar to his Creator: he can know things as they really are (thanks to his intellect), and he can freely love things (thanks to his will). No sub-human animal, not even an anthropoid ape, has any ability that comes close to this.

* It should be specified that, because human beings are spiritual creatures, it is beyond the capacity of human parents to produce a new human being. The best that they can do is prepare the necessary “matter” that can receive a human soul; it is God, however, Who directly creates each human being as such.