St. Nicholas Church Altar Apparition

A see-through man stands before an altar at St. Nicholas Church. Is it a real apparition or were two photographs transposed, one over top of another?

The famous photograph was taken in 1940 in Arundel, Sussex, England.

Whether or not it is a real apparition photograph has been debated over several decades. Examine it closely...

If not a ghost, was it made by way of a photographic double-exposure?

Or maybe the photo was made with lengthened-exposure and by having someone stand in front of the church altar just long enough to appear transparent.