Very few ancient painted portraits survive. Bronze statues were melted down for their metal, so most of those we have are marble. And paintings tended to be on fragile materials that have been eaten away by the centuries. I know people were quite surprised by the 'modern' quality of the drawings in the Artemidorus Papyrus, so I thought it might be worth highlighting some information about ancient 2-D portraits. Aba of Caria was probably represented on the wall of the tomb of Hecatomnus.
Many portraits on wooden panels survive from Egypt, but these tend to be the mummy portraits of private individuals. This tondo is more interesting as the head-gear worn by the family show that it represented royals, and the style of dress that they were Roman, so it depicts the Imperial family.
The face could be Clodius Albinus or Septimius Severus - the two can look very similar - but the bifurcate beard shows that it is the later. Sometimes the two strands of the beard were even longer and more pronounced, a portrait type known as the Septimius-Serapis type because of its similarity to depictions of the god Serapis.
Septimius Severus was an 'African' emperor in the sense that he was descended from Romans that had settled at Lepcis Magna in Libya, but the extend to which he had native or Berber blood is a matter of conjecture. The tondo shows him as having browner skin than his wife, but brown men and white women were a convention of ancient art seen in Egyptian and Minoan paintings.
Some portraits show Septimius Severus with a gaunter face or longer beard, but this head from Herculaneum in the Louvre of the Septimius-Serapis portrait type is the closest I could find to the tondo portrait.
And if you want to see some non-marbles images of Caracalla, then Google the Aboukir Medallions for an image of the adult brute that he became (article, see also images of Alexander the Great and Olympias in Berlin)