WSC Q.51: What is forbidden in the second commandment?
The second commandment forbiddeth the worshipping of God by images, (Deut. 4:15–19, Exod. 32:5,8) or any other way not appointed in his Word. (Deut. 12:31–32)
WLC Q.109: What are the sins forbidden in the second commandment?
The sins forbidden in the second commandment are, all devising, (Numb. 15:39) counselling, (Deut. 13:6–8) commanding, (Hosea 5:11, Micah 6:16) using, (1 Kings 11:33, 1 Kings 12:33) and any wise approving, any religious worship not instituted by God himself; (Deut. 12:30–32) the making any representation of God, of all or of any of the three persons, either inwardly in our mind, or outwardly in any kind of image or likeness of any creature whatsoever; (Deut. 4:15–19, Acts 17:29, Rom. 1:21–23,25) all worshipping of it, (Dan. 3:18, Gal. 4:8) or God in it or by it; (Exod. 32:5) the making of any representation of feigned deities, (Exod. 32:8) and all worship of them, or service belonging to them, (1 Kings18:26,28, Isa. 65:11) all superstitious devices, (Acts 17:22, Col. 2:21–23) corrupting the worship of God, (Mal. 1:7–8,14) adding to it, or taking from it, (Deut. 4:2) whether invented and taken up of ourselves, (Ps. 106:39) or received by tradition from others, (Matt. 15:9) though under the title of antiquity, (1 Pet. 1:18) custom, (Jer. 44:17) devotion, (Isa. 65:3–5, Gal. 1:13–14) good intent, or any other pretence whatsoever; (1 Sam. 13:11–12, 1 Sam. 15:21) simony; (Acts 8:18) sacrilege; (Rom. 2:22, Mal. 3:8) all neglect, (Exod. 4:24–26) contempt, (Matt. 22:5, Mal. 1:7,13) hindering, (Matt. 23:13) and opposing the worship and ordinances which God hath appointed. (Acts 13:44–45, 1 Thess. 2:15–16)