A crucifix is an example of a forbidden idol. Especially the great big ones ina church people kneel and bow before.
Not to bow down to an idol, even if that is not its mode of worship (Ex. 20:5)
Not to worship an idol in the way in which it is usually worshipped (Ex. 20:5)
Not to swear by an idol to its worshipers, nor cause them to swear by it (Ex. 23:13)
Relevant one here,
Not to set up a pillar (for worship) (Deut. 16:22)
No, a crucifix is not an example of a forbidden idol. Keep in mind that in Old Testament times, people made graven images (think golden calf) to worship. There were engravings on the Ark of the Covenant, but they did not qualify as idols--they were not worshiped, no one thought they had powers. They simply represented the power and holiness of God.
Catholics do not believe the crucifix has power, the belief is that Christ has power, and the crucifix represents the sacrifice he made for us. It is an object of reflection and contemplation--it helps keep the mind and spirit focused on God.