|Image from http://archaeologyinbulgaria.com/|
There are several fascinating features of these images. What I found initially striking was that Jesus is young, beardless, has short(ish) hair, and robed. All of these features parallel another 4th-century find.
This glass plate found in Linares, Spain shows a similar Jesus with the notable difference of an aureole (i.e. the plate shows Jesus with a halo; the painted tomb does not). Similar portraits of Jesus can be found in the Roman catacombs. So when did Jesus become the long-haired, bearded man, in a stolē rather than a chitōn (cf. John 19:23)? Joan Taylor's article surveys a few interesting developments in Jesus' appearance.
For an almost credible reenactment of what the early Christians thought about the importance of beards, see here.