The coins of Justinian II’s first reign (685 – 695 AD) are indeed remarkably shroud-like, and it is difficult not to think it was indeed the model. However, when, after a period of exile, Justinian returned to the throne (705 – 711 AD), the same sort of coins (with the same designation – Christus Rex Regnantium) have a closely shaven Christ with tightly curly hair. Can anyone suggest why the changed their mind about Christ’s appearance?
This image from the emperor’s second reign, A. D. 705-711 shows Justinian II with Tiberius on the reverse side. The obverse side shows Christ with curly hair and short, trimmed beard.
Later coins, for instance during the reign of Romerus II with Constantine VII and if not before, show Christ again with long flowing hair and a full beard.