From the Dogmatic Decree of the Second Œcumenical Council of Nicæa:
We keep unchanged all the ecclesiastical traditions handed down to us, whether in writing or verbally, one of which is the making of pictorial representations, agreeable to the history of the preaching of the Gospel, a tradition useful in many respects, but especially in this, that so the incarnation of the Word of God is shown forth as real and not merely fantastic, for these have mutual indications and without doubt have also mutual significations.
We, therefore, following the royal pathway and the divinely inspired authority of our Holy Fathers and the traditions of the Catholic Church (for, as we all know, the Holy Ghost indwells her), define with all certitude and accuracy that just as the figure of the precious and life-giving Cross, so also the venerable and holy images, as well in painting and mosaic as of other fit materials, should be set forth in the holy churches of God, and on the sacred vessels and on the vestments and on hangings and in pictures both in houses and by the wayside, to wit, the figure of our Lord God and Saviour Jesus Christ, of our spotless Lady, the Mother of God, of the honorable Angels, of all Saints and of all pious people. For by so much more frequently as they are seen in artistic representation, by so much more readily are men lifted up to the memory of their prototypes, and to a longing after them; and to these should be given due salutation and honorable reverence, not indeed that true worship of faith which pertains alone to the divine nature; but to these, as to the figure of the precious and life-giving Cross and to the Book of the Gospels and to the other holy objects, incense and lights may be offered according to ancient pious custom. For the honor which is paid to the image passes on to that which the image represents, and he who reveres the image reveres in it the subject represented. For thus the teaching of our holy Fathers, that is the tradition of the Catholic Church, which from one end of the earth to the other has received the Gospel, is strengthened. Thus we follow Paul, who spoke in Christ, and the whole divine Apostolic company and the holy Fathers, holding fast the traditions which we have received. So we sing prophetically the triumphal hymns of the Church: Rejoice greatly, O daughter of Sion; Shout, O daughter of Jerusalem. Rejoice and be glad with all your heart. The Lord has taken away from you the oppression of your adversaries; you are redeemed from the hand of your enemies. The Lord is a King in the midst of you; you shall not see evil any more, and peace be unto you forever.
Those, therefore who dare to think or teach otherwise, or as wicked heretics to spurn the traditions of the Church and to invent some novelty, or else to reject some of those things which the Church has received (the Book of the Gospels, or the image of the cross, or the pictorial icons, or the holy relics of a martyr), or evilly and sharply to devise anything subversive of the lawful traditions of the Catholic Church or to turn to common uses the sacred vessels or the venerable monasteries, if they be bishops or clerics, we command that they be deposed; if religious or laics, that they be excommunicated.
So we all believe, we all are so minded, we all give our consent and have signed. This is the faith of the Apostles, this is the faith of the Orthodox, this is the faith which has made firm the whole world. Believing in one God, to be celebrated in Trinity, we salute the honorable images! Those who do not so hold, let them be anathema. Those who do not thus think, let them be driven far away from the Church. For we follow the most ancient legislation of the Catholic Church. We keep the laws of the Fathers. We anathematize those who add anything to or take anything away from the Catholic Church. We anathematize the introduced novelty of the revilers of Christians. We salute the venerable images. We place under anathema those who do not. Anathema to those who presume to apply to the venerable images the things said in Holy Scripture about idols. Anathema to those who do not salute the holy and venerable images. Anathema to those who call the sacred images idols. Anathema to those who say that Christians resort to the sacred images as to gods. Anathema to those who say that any other delivered us from idols except Christ our God. Anathema to those who dare to say that at any time the Catholic Church received idols.