Joe Vusich explains why the Second Commandment does not forbid all images but does forbid images of the Trinity. I have excerpted a couple of his points below.
First, Mr. Vusich explains that the language of the Second Commandment specifically targets the worship of the Egyptians, with which the Israelites were familiar:
2. Egyptian gods corresponded to “heaven above (sky gods) . . . the earth beneath (animal gods) . . . and the water under the earth (river and underworld gods).
Also, based on the context of the passage, both historically and religiously, Mr. Vusich demonstrates that the Second Commandment is not meant to be a general prohibition on all images but rather a prohibition on making religious images:
6. Thus the 2nd Commandment was never intended as a general decree forbidding the creation of every sort of image, but a two-imperative law that forbade 1) making images of beings that are worshiped; and 2) the worship of those images.