But, there were only 29 people standing in front of the camera, while 30 faces can be seen looking into the lens.
The picture was taken by ghost hunter Phillip Barron, 45, before the group set out to investigate the former Grade II listed asylum in Newsham Park, near Liverpool.
He says the image shows the figure of a girl in the middle who was not part of the trip, and nobody knows who she is.
The ghost hunter claimed no-one else was there and no-one remembered seeing the mystery girl.
He said: “I have never come across anything like this before.”
Readers of the Liverpool Echo, which first ran the story, have mixed views on it.
Some have claimed it must be a hoax, while others believe it could be something paranormal.
The girl, circled, appears to be clear, but in a different light to the rest of the group.
One reader even claimed to see another face below her, and possibly a third nearby.
Sceptics claim that images like this are the result of pareidolia.
This is when the brain tricks the eyes into seeing familiar objects like faces in patterns or textures.
Coupled with a strong imagination, people see what they want to see, it is claimed.