Answer: They are different because one is hyperrealistic and another one is realistic. Both of them are showing the seriousness of mind and attitude that was important to Roman culture.
Step-by-step explanation:
The artwork on the left side is representing a portrait statue of the Head of a Roman Patrician from Otricol and the artwork from the right is representing Augustus of Prima Porta( full-length portrait of Augustus Caesar).
The face of Augustus Caesar in this image is idealized and it is realistic and it is representing the Roman Republican Era. On the other side, the Head of a Roman Patrician is hyperrealistic and it is representing the face of a Roman aristocrat. His portrait is representing something that was very important to Roman aristocrats and that was the seriousness of mind and also virtue.