In 1951, somebody gave the Ashmolean Museum at Oxford a postcard-sized oil painting on wood said to be by Rembrandt.
In 1981 it was examined and dismissed as an imitation by the Rembrandt Research Project and hidden away.
“They saw it in the flesh and decided it wasn’t a Rembrandt painting,” Ashmolean curator An Van Camp explained to The Guardian. “They said it might be an imitator painting in the style of Rembrandt and is possibly made before the end of the 17th century, so not even in Rembrandt’s lifetime.”
The painting was placed in the basement
But the painting is now back on display after study showed that it was from the same piece of wood as another, more famous and well authenticated Rembrandt work. (Wooden panels for paintings were made by splitting wood into thin pieces, so you can sometimes line up the irregularities in the wood and show they are from the same tree.)
These people who think they can tell who painted a picture just by looking at it, they are wrong. Of course it isn't a very good painting, but for mysterious reasons that matters not at all compared to who painted it.