Upvote:3
From the first two commandments:
Exodus 20:3-5a (ASV)
Thou shalt not make unto thee a graven image, nor any likeness [of any thing] that is in heaven above, or that is in the earth beneath, or that is in the water under the earth. 5 Thou shalt not bow down thyself unto them, nor serve them
I think this very clearly describes what is meant by "graven image" ("idol" in other translations): an object of worship, or the representation of such a an object used as a part of worship.
There is not uniformity among Christians regarding to what extent the Law of Moses affects us. This answer does a good job of summarizing the most common views. Someone who believed that the Law of Moses was give to Israel and is no longer binding might not feel compelled by the second commandment in this regard, because it has at its core the worship of things that aren't God (and perhaps attempting to represent God in some form—but that is a much larger discussion).
People who have these images/icons in their assemblies or around their necks would not say that they worship them or use them as representatives of God to worship, distinguishing between "veneration" (δουλεία, 1397) and "adoration" (λατρεια, 2999).
Included in this article is a reasonable defense of the practice: My Bible study group asks, “Why does the Catholic religion portray Jesus hanging on the cross while Protestant crosses are empty?”