"Brown Lady of Raynham Hall" ghost photo

Some older books offer “evidence” of ghosts with a photo taken in the 1930’s at Raynham Hall (England, near Norwich, I think). The photo shows a blobby figure that is said to be the ghost decending the stairs. Kinda spooky, but not exactly convincing.
Anyway, has the photo ever been explained or debunked? Did the photographers ever come forward and say they were pulling a fast one?

Duplicate thread.