A dark room, an old camera - and suddenly a silhouette appears in the picture that was not there in reality.
Stories like these seem like fiction until you see the evidence.
The museum archives contain dozens of 19th century photographs of mysterious figures.
One of them shows a girl in a Victorian dress sitting on an empty bench. But when the photo was taken, the park was deserted.
Modern technologies have eliminated forgery: the images were not edited.
Another shot is a child's portrait from the 1920s, where a translucent hand is visible behind the child's back.
X-ray analysis showed that the hand was not painted or glued on.
Ufologists talk about portals to other dimensions, physicists - about light anomalies. But no theory explains why ghosts most often appear in the frame by accident, as if not wanting to be seen.
Modern cases are no less strange. In 2018, a tourist photographed an abandoned castle in Scotland.
The photo shows a man in medieval clothing in the window. But the building was closed to visitors and infrared sensors did not detect any movement.
Another example is a selfie of a girl in the forest, where behind her stands a translucent figure with a distorted face.
Experts checked the metadata: the photo was not edited.
Is this a trick of the light, a mass hallucination, or evidence of the otherworldly?
Scientists continue to argue, but one thing is clear: some secrets still remain beyond our understanding.
