The camera, which was disguised as a plastic clothes' hook, was discovered by two schoolgirls on Thursday morning.
"It is disgusting to think that someone has hung a spy camera in the girls' shower, with the clear purpose of filming us naked," Malene Austad, one of the girls, told VG newspaper.
Ingrid Wiik, a lawyer with the local Telemark police, said that officers had carefully scrutinised the video footage the high-tech peeping tom had saved onto the disc.
"We have gone through the material on the camera, and as far as we can understand it seems like it was discovered pretty quickly," she said.
She confirmed that the perpetrator had stepped into the frame as the device began recording.
"We have a picture of part of his face," she told VG. "As he pressed the button to start recording, he snapped a picture of himself."
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The police are encouraging students down to the station to examine the footage and see if they can identify the boy.
"We assume that he belongs to the school, and we hope students can help us," Wiik said.