“We decree with full precision and care that, like the figure of the honored and life-giving cross, the revered and holy images, whether painted or made of mosaic or of other suitable material, are to be exposed in the holy churches of God, on sacred instruments and vestments, on walls and panels, in houses and by public ways; these are the images of our Lord, God and Savior, Jesus Christ, and of Our Lady without blemish, the holy God-bearer, and of the revered angels, and of any of the saintly holy men.”

Second Council of Nicaea (Seventh Ecumenical Council) - 787 A.D.

In iconography an icon is not painted, but written. The process of writing an icon is long and tedious. Many hours, weeks, sometimes months are spent in the creation of an icon, depending of course on the size and complexity of it. A Russian monk remarked once that "...icons are not civil paintings. They are not for museums. They are not decorations. They are a reflection of God that has become man. Icons carry the real feeling and teachings of Orthodoxy."
Here you can read more about the process of writting the icons.

The iconographer, just as all Orthodox Christians, must be humble of heart. Purifying his heart will enable him to see clearly his task. Or rather so that he may have the Holy Spirit dwelling in him fully, in order to allow God to work through Him. If a mans heart desires the things of the world then he cannot comprehend the mystery, or the beauty of the spiritual and sanctified world. The iconographer is a tool. The Holy Spirit is the conductor, the guide. The paint brush is empty and is useless, unless the painter picks up the brush and guides it along. It is the same with the iconographer. The iconographer is like the brush, and the Holy Spirit is the conductor.

In iconography there are two distinct categories of colors. First there is white, red, green and blue, used to express life, purity, peace and goodness. The second category of colors is black, brown, grey and yellow, and they are used to express danger and impurity. You can read more about this subject here.

Iconography began in the Old Testament. Images were indeed permitted in the Scriptures. The Hebrews did not create images of God, because no one had ever seen Him: "And the Lord spake to you out of the midst of the fire a voice of words, which he heard, and ye saw no likeness, only a voice." [Dt.4:12]

But while at the same time God spoke to Moses, giving him a command: "And thou shalt make a mercy seat, a lid of pure gold, the length of two cubits and a half, and the breadth of a cubit and a half. And thou shalt make two cherubim graven in gold, and thou shalt put them on both sides of the mercy seat. They shall be made one cherub on this side, and another cherub on the other side of the mercy seat, and thou shalt make the two cherubim on both sides. The cherubim shall stretch forth their wings above, overshadowing the mercy seat with their wings; and their faces shall be toward the mercy seat." [Ex.25:17-22]

Since God Himself allowed us to see what the cherubic angels looked like, they could now be represented in form by us. But not only the images of the two cherubims were seen as icons, but the Tabernacle itself, the icon or image of Heaven , the Holy of Holies, the Throne of God, from where God spoke to man. Later God made himself a man. Now, not only had we seen God in the flesh, but we had seen His face. Now there was a certain obligation to make an icon of God in the flesh as a means of education and veneration. We cannot separate God from Jesus Christ; it is impossible to create an icon of Christ without, at the same time, making God present.

The icon is not nearly a piece of art, but an aid to worship, and an instrument for the transmission of Christian tradition and faith. The Holy Spirit speaks to men through icons. Anywhere an icon is placed a place of worship and prayer is set, because the icon is not an end in itself, but a window through which we look with our physical eyes at the Kingdom of Heaven and the realm of spiritual experience. It is important to remember thus that the icon is concerned only with the sacred; the icon is theology in images and color.

Along with the Holy Scripture, the icon is a tool for the transmission of Christian tradition and faith. The Holy Spirit speaks to us through the use of images, images that are complementing the written words of the Scripture. It follows then that icons are educational and worshiping aids. This is why it is important to mention that the faith of the person who prays is above the aesthetic qualities of an icon. For the Orthodox Christian the icon is not an aesthetic object, or an object of study. It is meant to transfigure and to inspire the person to prayer and contemplation. The icon has as its purpose to transport us into the realm of spiritual experience, to go beyond our material world, to show us the greatness and perfection of the divine reality that is invisible to us.

The icon is not meant to be a sentimental piece. There is no sentimentality or drama in an icon. An icon represents mostly biblical events and biblical characters. The faces of those depicted in an icon are always devoid of their feelings, suggestive only of virtues such as: purity, patience, forgiveness, compassion and love. For example, the icon of the Crucifixion does not show the physical pain Christ suffered on the Cross, but what led Him to the Cross: the voluntary action of giving His life for us.

Icons are also silent. A close observation indicates that the mouths of the characters depicted are never open; there are no symbols that can indicate sound. There is perfect silence in the icon and this stillness and silence creates, both in the church and in the home an atmosphere of prayer and contemplation. The silence of an icon is a silence that speaks, it is the silence of Christ on the Cross, the silence of the Virgin, the silence of the Transfiguration, the silence of the Resurrection.

Icons are not three-dimensional. Perspective in the icon does not exist. The attempt is made to suggest depth, but the frontal plane is never abandoned, because the icon is not a representation of our conscious world, but an attempt to suggest the beauty of the Kingdom of God. Natural objects are therefore rendered in a vivid but symbolic, sometimes an abstract manner, because spiritual reality cannot be represented in images, except through the use of symbols. As an example, an icon of the Baptism of the Lord depicts Christ as a young man, even though He was a fully matured man at the time of His baptism in the Jordan. The meaning is that through baptism we enter a new life. Also in this icon (mosaic) of the Baptism we see an old man sitting opposite John. He represents the Old Jordan River. The Holy Spirit descending upon Christ is depicted as a white dove.

The person depicted in the icon is a new person who regardless of sex is a reflection of the New Man Jesus Christ. Through the incarnation the invisible became visible and the undepictable became perceptible and therefore depictable. The icon, therefore, depicts each person as a new being who has been restored to God's image and likeness. For this the icon is able to become an object evoking contemplation and prayer from the one who views it. Because of this, Orthodox iconography can only be properly appreciated in the context of communal prayer which provides the basis for its content and form. Iconography is an art that springs from the liturgical celebration of the new covenant, The Eucharist established between God and man through the Incarnation of Jesus Christ who says: "Behold I make all things new" (2Cor. 5:17).

In an icon history and eschatology are brought together. Everything is depicted as existing beyond time and space. Everything in the icon is on one single plane, figures are long and thin, the center of gravity is upwards and not downwards. The icon is able to witness to the liberation of what is evil and oppressing in this world and reveals human beings as created in the image and likeness of God. This tells us that man has the capacity to know and change creation, because man, like God is able to love.

The icon is to be a means of contemplation and prayer the one standing in front of it must be willing to enter a process of repentance which can be painful. Standing before the icon and seeing it for what it is, makes us realize the state of brokenness we are in and our alienation from God. Contemplating the icon requires repentance which is a conversion from that self-destruction to life. If we can contemplate the icon in silence we will enter a state of sorrow and joy.

In the presence of a good icon we move from contemplation to prayer. In fact it is said that a good icon is one that inspires prayer. The mind, soul, heart, body and will of the person who prays becomes still, attentive, attuned, and peaceful, constantly receptive to the presence of God.

As we pray before an icon we enter in communion with the icon's prototype. This becomes the fulfillment of Christ's prayer: "so that they all may be one, as You, Father, are in Me, and I in You; that they also may be one in us..." (Jn 17:21).