A pair of aspiring paparazzi staked out two weddings in Seoul's high-end Gangnam district recently, but they weren't looking for celebrities. Their target: officials receiving gifts that might violate South Korea's tough new anti-corruption law.

About 4 million people are estimated to be directly covered by the law — civil servants, employees at state-owned enterprises, teachers, journalists — which limits the value of meals and gifts that can be accepted.

With rewards worth up to 200 million won ($181,691), it is also fueling a cottage industry of camera-wielding, receipt-scavenging vigilantes targeting expensive restaurants and fancy weddings in a country with a deep tradition of entertaining and gift-giving.