Fake or fortune? Edgar Degas' Blue Dancers
14 September 2012 Last updated at 19:25 BST
Discovering a new painting by one of the world's most renowned artists is something art experts dream of - yet happens rarely.
But cutting edge forensic techniques are making it possible to establish the authenticity of pictures in ways not thought possible before.
As a result paintings by some of the great masters that were either unknown or considered fakes are now being re-evaluated.
The BBC's Fiona Bruce follows the investigation of a painting by one of France's best loved artists, Edgar Degas.