SEOUL — With his debts mounting and his wages barely enough to cover the interest, Im Hyun-seok decided he needed a new job. The mild-mannered former English tutor joined South Korea’s growing ranks of camera-toting bounty hunters.

Known here sarcastically as paparazzi, people like Mr. Im stalk their prey and capture them on film. But it is not celebrities, politicians or even hardened criminals they pursue. Rather, they roam cities secretly videotaping ordinary citizens breaking the law, deliver the evidence to government officials and collect the rewards.