Eastern Christian theology of iconography:
The word "icon" (εικονα) etymologically derives from the verb "ico" (εικω) or "eica" (εοικα) which means "likeness" (or image), namely an imprint of the characteristics of the prototype. This means that an icon does not have its own hypostasis (being) but its value exists in the likeness with the prototype. "For what is imprinted is different from that which is being imprinted" says Saint John Damascene. The icon therefore is the perceptible means between the faithful and the prototype which is invisible to them. Great Basil refers to a distinction between a "natural" and "artificial" icon. Both types of icons have a common known, the likeness of the prototype that they depict. They differ though in this: The likeness of the natural icon to the prototype refers to the essence of the depicted prototype, maintaining the difference in its hypostasis. A characteristic example of a natural icon is the Son and Word of God in relation to God the Father. The Apostle Paul says that "Christ is the icon of the invisible God" (Col 1:15). Namely, the Son is "the identical icon of the Being" as Saint John Damascene mentions, and referred to God the Father as being identical in essence. What makes the Son different to the Father is His hypostasis and specifically the characteristic of being born. On the other side, the artificial icon likens the depicted person in his appearance but differs as of his essence. Since the artificial icon refers only to the appearance of the one depicted, therefore what is depicted is not his nature but the hypostasis of the prototype as mentioned by Saint Theodore Studite: "What is depicted on an icon is not its nature but its hypostasis". This likeness between the icon and the one depicted constitutes the condition of existence of the artificial picture. That is why the Orthodox icons are not a product of the fantasy of every artist but the prototypes (the Lord, the Theotokos, the Saints) are historic personalities with their own individual characteristics. Clearly the Fathers of the 7th Ecumenical Synod observe, "Having seen the Lord, as they saw, so they depicted Him, and having seen James, the brother of the Lord, as they saw him, so they depicted him".
- from "Theological approaches to the Hagiographic art" cited 12 Oct. 2010 from the website of the Holy Monastery of the Pantocrator: http://www.impantokratoros.gr/751A636C.en.aspx