The Lord Jesus Christ became the first iconographer by 'writing' his image on the three 'not-made-by-hands' relics. Because an icon is a holy image, not just a work of art, iconographers undergo spiritual as well as technical preparation. The Orthodox Church regards the vocation of iconographer as serious a call, similar to that of a religious or priestly vocation. The Russian Orthodox Church gives a ceremonial benediction before the trained iconographer begins his or her work.
Fasting, prayer, confession and communion are spiritual tools employed in writing the icon. Painting methods, materials styles are all regulated by Church tradition. Formal training is indispensable.
Eastern Orthodox iconographers who adhere to the traditional techniques and spiritual practices of icon writing...who write icons as their vocation...truly produce a holy image and a blessing is not required.
This is not necessarily the case with modern icons written by artists who adhere to traditional style but not religious practice, as well as icon prints which are not painted at all. These are often blessed by a priest with prayers, holy water and sometimes by keeping them in church Sanctuary area for 40 days (depending on the Orthodox jurisdiciton).
This page has more detailed information.