Catechism of the Catholic Church §1159 — excerpt
The sacred image, the liturgical icon, principally represents Christ. It cannot represent the invisible and incomprehensible God, but the incarnation of the Son of God has ushered in a new "economy" of images:
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Also cites: St. John Damascene, De imag. 1, 16: PG 96: 1245-1248