While most artworks derive their value primarily from the artist's reputation, portraits are an exception. In portraiture, the identity and historical significance of the subject is what determines the artwork's value—not the artist who painted it.
In the case of portrait paintings, it is not who painted it that determines its value—it is who the painting represents.
Unlike other genres, portraits are valued based on who is portrayed, not who painted them. When the subject is a prominent historical figure—such as a renowned composer, explorer, or political leader—their identity can elevate the portrait's value, regardless of the artist's renown. This is especially true when authentic, original likenesses of such figures are rare or scarce.
For instance, there are only five known portraits of Wolfgang Amadeus Mozart dating from his lifetime. As a result, any newly discovered portrait that can be convincingly authenticated as having been painted during Mozart’s life could easily exceed $5 million in value, regardless of the artist that painted it.