Cunning croc snapped... on film

Kyle MacLennan didn't realise until days later that he made a lucky escape from this crocodile in the harbour at Mandorah. Photo / Supplied

It's become the ultimate holiday snapshot.

An Australian woman photographed her 26-year-old son swimming in a marina in the Northern Territory settlement of Mandorah - and only later was amazed to see an extra figure in the photo.

The image shows a crocodile eyeing Kyle MacLennan as he swims towards a small boat.

"No one even knew it was there," Mr MacLennan told the Northern Territory News.

"I was completely unaware until I saw the pic."

Mr MacLennan's mother, Lui, did not look at the photos until she returned to Sydney days later.

"I was really hoping it was a practical joke being played by my mum," he said. "But she assures me it wasn't. It looks like it was looking right at me. It's not that huge."

Mr MacLennan said he and his mother had been touring Mandorah and photographing lighthouses for his mum's friend for an upcoming book. "It was a couple of days later when they got back to Sydney [that they saw the photo]," Mr MacLennan told the Northern Territory News. "There were a couple of frantic emails. [Mum] is always telling me to be safe."