Forty-two-year-old John Martin of Wenonah pleaded guilty to invasion of privacy and child endangerment on Thursday.
Martin was chief custodian at Gloucester Catholic High School until he resigned in November.
Martin admitted placing the pinhole-size cameras in ventilation ducts and smoke detectors in eight rooms that were often used as changing areas. Martin linked the cameras to the school's video security system at Gloucester Catholic.
Some of the images showed nudity.
Martin faces a term of parole supervision for life when he's sentenced in December.
