Postcard - sized painting was bought as part of a larger lot at auction for $ 46 ( £ 30 ) Art historians believe it is a painting by English artist John Constable , worth $ 390,000 ( £ 40 ) `` I was over the moon but also shocked when I found out what the painting really is . Painting is thought never to have been on public display before .
Postcard - sized painting was bought as part of a larger lot at auction for $ 46 ( £ 30 ) Art historians believe it is a painting by English artist John Constable , worth $ 390,000 ( £ 40 ) Painting is thought never to have been on public display before .