Exodus 20:4 "Thou shalt not make unto thee any graven image, or any likeness of anything that is in heaven . . . earth . . . water." (See also Lev. 26:1, Deut. 27:15)
A clear enough command, the Skeptics say -- so why these?
Exodus 25:18 "And thou shalt make two cherubims of gold, of beaten work shalt thou make them."
I Kings 7:15,16,23,25 "For he [Solomon] cast two pillars of brass . . . and two chapiters of molten brass . . . And he made a molten sea . . . it stood upon twelve oxen . . . [and so on]"
Question: WHY were the Israelites commanded not to make graven images?
Answer: Graven images were the standard method of pagan worship. They were representations of false gods.
Now that being the case, it is fairly obvious that an "image" NOT made for worship is acceptable. In fact, we should not really call things like the cherubims "images" at all -- an "image" in ancient thought is not merely something that has an appearance, like a statue or a picture, but something that serves as a focal point for the presence and power of a deity.
Thus for example ancient rulers in Egypt, Babylon, and elsewhere were referred to as the "image" of a certain deity, not because they looked like the deity, but because the deity's power and authority was thought to operate through them. The critic is simply making the same erroneous interpretation that much of Jewish culture made.
(Though I credit that to Jewish culture as an instance of erring on the side of caution, rather than a full-fledged error. It has been noted that Jewish excellence in poetry and music may be attributed partially to the above commands. For more on the use of the word "image", see Chapter 1 of my book, The Mormon Defenders.)
Solomon's bulls and such were (as far as we can tell) not for worship and do not fit the definition of an "image" we have described. The cherubim on the Ark were not for worship and also do not fit the ancient definition. So, the command was not violated in either case.
We should add that the Hebrew words for "image" and "likeness" are essentially synonyms (as shown both by their interchangeable use in the OT, and by the interchangeable use of the equivalent words in pagan literature of the period), and a "likeness" is also therefore a focal point for the presence and power of a deity, just like an image.
-JPH