Each of us has at least once heard or said an expression “icon-painting face”. What kind of faces are they talking about? Regular features and elongated shape of the face; inspired, as if not from this world, eyes; thin nose; big forehead. This may surprise: were all the saints alike? That is, did they really have just such an “icon-painting appearance”, despite the fact that they were born in different families, different countries, belonged to different races?
Of course not. The saints looked completely different, and their holiness was in no way connected with a certain type of appearance. The fact is that image of a saint on an icon is not a portrait, and icon itself is not the most accurate fixation of physical reality. An icon painter sees far beyond individual traits. Although it is quite possible to recognize the features of a real prototype – a historically existing saint – on a icon, we do not see a portrait of this man, but, so to speak, a portrait of his soul. A reflection of the Holy Ghost in the eyes, the experience of communication with God, love and compassion for people, love for Christ.
Of course, the style of an icon-painting school in which this or that face of a saint was written plays a role. The choice of colors and the overall color tone of the icon, the way to create the image, compositional features – everything plays a role. On the icons painted in one tradition, the face of the Savior is dark, solemn and kind of strict; in another tradition – with softer features, made in pastel shades and kind of permeated with light. But despite the stylistic differences, on each of the icons is the very Christ, the only one who atoned for our sins by His death on the cross and rose. This is the miracle of icon painting – this is not portrait painting, but art that dares to portray the eternal, divine.
Source: https://foma.ru/pochemu-na-ikonah-vse-svyatyie-pohozhi-drug-na-druga.html
Saints were real people. Their faces and physical features were unique to each as their level of spiritual condition. Each is reflective in the icon. No, icons are not portraits but we do paint each particular Saint with their particular attributes. How do we recognize Saint Nektarios, Saint George the Great Martyr, Saint Mary of Egypt, Saint Xenia? Some Saints we do not know as well as others but we use text, photographs, whatever we can find as aid. If nothing can be found to help guide us, as iconographers we say our prayers, and ask The Holy Spirit and the Saint for guidance. If icons are given generic assembly line features that one Saint can not be distinguished from the other, in other words all exactly alike then that is just poor iconography.