A federal judge in LA ruled that a Spanish museum that acquired a priceless, Nazi-looted painting in 1992 is the work’s rightful owner, and not the survivors of the Jewish woman who surrendered it 80 years ago to escape the Holocaust

The plot twist was the painting was an original Hitler painting.

What makes this painting "priceless"? I'm sure if this went up for auction it would be sold at a price. One of a kind and rare? Almost every painting is by that definition? By a famous artist? Plenty of famous artists have huge libraries of works and many of those are completely forgettable and only receive attention because of their creator. What makes a piece of art priceless?