Locals at The Gin Mill pub in Arklow do not recognise the phantom punter and have no recollection of seeing the man on the day.
Adrian has strongly refuted any suggestion that the pictures have been tampered with.
"The pictures are 110pc genuine," he said.
"The leading expert on photography in the world is free to come down and examine the photos. They haven't been touched."It would have been difficult in the past to super-impose an image on to a photograph, but it can be done nowadays.
"Why would I bother in conjuring this up on a computer when anyone with knowledge of computers and photography could do it
"We have the raw files, which can be examined by any labs."
Meanwhile, staff at the pub are especially interested in locating the ghostly figure, to bar him for smoking in the premises, as the man appears to have a pipe.
"There is a blown-up copy of the photo in the bar and nobody has the faintest idea of who it is," said a barmaid, who was working on the day the photo was taken, September 24.
"The plan was to take a photo to mark the occasion. It's so weird.
"I certainly didn't serve him on the day."
Mr O'Brien, a photographer, admitted to be shaken up about the photo and that his studio in Arklow has been engulfed with people trying to identify the elderly man.
"It's created a mad buzz," he said. "We have loads of people coming into the office to view the pictures to see if it's their dead relation.
"I don't believe in ghosts or anything, but this has sent shivers down my spine"
Even the most ardent believers in the paranormal are sceptical as to whether this image is that of a ghost.
Brian Gallagher, of Leinster Paranormal, an organisation which investigates paranormal activity using "logic before paranormal", can't be sure of what was captured on camera that day.
"We see this sort of thing very often" he said.
"To be certain, we would have to interview everyone involved, but it is likely the person in the picture is not a ghost but a reflection of some sort.
"Of course, we cannot be 100pc sure about its authenticity, but at this early stage I would be sceptical."