From the Heidelberg Catechism, for the Lord’s Day, September 8

96. What does God require in the second Commandment?

That we in no way make any image of God, nor worship Him in any other way than He has commanded us in His Word.

97. May we not make any image at all?

God may not and cannot be imaged in any way; as for creatures, though they may indeed be imaged, yet God forbids the making or keeping of any likeness of them, either to worship them or to serve God by them.

98. But may not pictures be tolerated in churches as books for the people?

No, for we should not be wiser than God, who will not have His people taught by dumb idols, but by the lively preaching of His Word.