Other offences were even more trivial, it says: one female former student was serving a term for having a western-style dance with a foreigner, another student was incarcerated for singing a South Korean song.
The report by the South's National Human Rights Commission, a state-appointed body, is its most detailed investigation of human rights abuses in the communist state. Officials provided extracts to AFP this week before its upcoming release.
"It details the horrific situation of inmates," a commission official said.
The report is based on interviews with 834 refugees, including those once held in the six camps, which rights groups say house a total of around 200,000 "political" prisoners.
It lists the names of 278 people in the camps between the mid-1990s and 2005 and information on their offences.
"We hope this report will have the effect of checking and preventing human rights abuses in North Korea," Lee Yong-Ken, head of the commission's North Korea human rights team, told AFP. Among the 278, about 60 prisoners -- the largest single category -- were being punished for fleeing the impoverished country in search of food and work abroad or for trying to escape to South Korea.
Twenty-seven of the inmates were ethnic Koreans who had settled in the North after moving from Japan.
Five people were imprisoned for