King's College in London says the portrait was probably painted by Joseph Hickel, who was a painter at Austria's imperial court. It says Hickel gave the portrait to Mozart in return for the composition of a serenade for a member of Hickel's family.
Eisen said he was able to authenticate the portrait by comparing it against auction records, archival documents and a letter written by the composer to his father in 1782.
He says the description in Mozart's letter matched the portrait down to the buttons.
