A tiny painting by John Constable has been rediscovered a decade after a retired consultant ophthalmic surgeon picked it up for $50 in a box of trinkets at auction.

The 19th-century landscape was bought by Robin Darvell, whose son recently took it to CNBC's "Treasure Detectives." The TV show's host, Curtis Dowling, appraised the painting as an original by the famed English artist whose well-known "The Hay Wain" is in the National Gallery in London.

Dowling gave the painting an appraised value of $388,000. He said, "In America, there is probably billions of dollars artwork or other antiques that people are sitting on without knowing it."

Constable's “The Lock,” from Madrid’s Bornemisza Museum, sold at Christie’s for $35 million last year.