The painting, discovered in the attic of Dorchester’s Mather Elementary School, had hung on the wall of Boston’s historic Parkman House for years. It was one of Mayor Thomas M. Menino’s favorites — a landscape of a sleepy Vermont town nestled in snow — but he knew little more about it than the artist’s name, Aldro Hibbard.

So the mayor did as any self-respecting American with a taste for the thrill of unearthing secret treasure would do: He took his find to “Antiques Roadshow.”