This is a good way to see how value is put on a "work of art"
http://newsfeed.time.com/2011/07/01/...o-be-unveiled/
It was sold in auction in 1958 for £45 (in today's money $120) even though it was thought to be by Leonardo Da Vinci's best student. today if auctioned they estimate it would fetch $120
million.
What has changed in the picture? The name of the painter and it's still known to be badly over painted. It's value is perceived. A pile of bricks or half a sheep are to you and me a pile of bricks and half a sheep. To some "art aficionados" they are priceless pieces of work. Even though their real value is in putting up a wall or roasting. Go figure.