North Korea has increased economic linkages with a prison camp where inmates are working by hand in agriculture, according to satellite imagery released today by a human rights group. The Committee for Human Rights in North Korea, a Washington-based group that is trying to shed light on the secretive state's record, said that Camp Number 25 near the northeastern city of Chongjin had about 75 acres (79 hectare s) of cultivated farmland including fields for grain crops,orchards and greenhouses.