whoes heads are who

[mdroberts18]

having come across a number of Greek and roman copies of Greek sculptured heads that are claimed as particular personalities but do not seem convincing i wonder if anybody knows how such ancient heads are attested if they do not have a name on them.The particular head that made me wonder is of Lysemachus the Hellenistic king of Thrace who seems to have two busts which look nothing like each other.I have seen roman emperors with names on the bust itself but most of these sculptures do not have such a name so how is it decided who they are .Looking forward to hearing suggestions
mike

[Giannis K. Hoplite]

The place and date is one thing.They make safe guesses.Comparioson with similar busts that do write the name on it is another thing. Some characteristics that are attributed to them may help. For example you'll always recognise an Alexander either in a coin,or in a bust of his time or a renaissanse one,because all have the same characteristics,even though most of them are imaginative.
Just some ideas.
Giannis