What's in a picture?
This is the so-called 'Severan Tondo', dating to c. AD 200 - i.e. roughly contemporary with events in 'The Consul's Daughter'. The painting depicts the emperor Septimius Severus, his wife Julia Domna and their two sons Caracalla and Geta. It's the only surviving wooden painting of its type: the material doesn't tend to resist the passing of the centuries even though this particular image would likely have been mass-produced to adorn offices and public buildings, and perhaps even private houses, throughout the empire.
Blood was apparently not thicker than water for Caracalla. Upon the death of Severus in 211, Geta was named co-ruler with Caracalla, who had become used to power since 198. Poor Geta didn't see out the year and was murdered in December. He suffered 'damnatio memoriae' after his death - an official blackening of his character - and his image was subsequently erased from paintings, and his name chipped from public inscriptions. The Severan Tondel is most probably an example of this harsh move.