SEOUL (REUTERS) - 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 four 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 (S$247,800), it is also fuelling 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.

Some of them come for training in the art of espionage at a school that calls itself the Headquarters of Reporting for Public Good, including the two that went to the weddings.

"You can get rich and become a patriot at the same time,"school president Moon Seoung Ok told students participating in a recent class that included tips on using hidden cameras.

"You can pick up credit card receipts from garbage at restaurants," he told his students at his classroom housed in an office near a Seoul courthouse, where he hands out booklets about the anti-graft law. "You need to obtain evidence."

THE 3-5-10 RULE

South Korea ranked 27th among 34 Organisation for Economic Cooperation and Development (OECD) countries in the 2015 Corruption Perceptions Index compiled by Transparency International.

Since the law took effect on Sept 28, golf course reservations have plunged and fewer guests are attending weddings, while hospitals have posted warnings against thank you gifts, media have reported. Some groups of diners are splitting bills - a practice once almost-unheard of in the country.

Consumer and entertainment companies could lose up to 11.6 trillion won under the law, the Korea Economic Research Institute said in June.

The law limits the value of meals that can be accepted by public servants and others to 30,000 won. Gifts are capped at 50,000 won in value, while cash gifts that are traditionally handed over in envelopes at weddings and funerals are limited to 100,000 won, under prohibitions now known as the "3-5-10" rule.

Violators can expect fines, but would face criminal prosecution for more serious infringements, such as receiving a gift of more than 1 million won, or for receiving a total of over 3 million won worth of gifts in a year.

Businesses are scrambling to adjust. The lobby group for the Korean conglomerates known as chaebol, the Federation of Korean Industries (FKI), held a seminar on Sept 8 attended by about 400 people on how corporate officials should comply with the law.

CHECK THE OBITUARIES

In South Korea, the term "paparazzi" applies not only to photographers chasing celebrities but to individuals who can win cash in other "report and reward" schemes that cover offences such as running traffic lights or dropping cigarette butts on the street.

The Kim Young Ran anti-bribery law, named after the former Supreme Court justice who proposed it, has spawned the term "ran-parazzi".

Mr Moon tells his students to find their way into weddings and funerals. "You have to look into who you are targeting," he said in an interview. "Check obituaries in newspapers to find out who's holding a funeral among the upper class."

While Mr Moon's school does not charge tuition for the"ran-parazzi" in training, it offers to sell students gadgets, including pens and spectacles with hidden cameras. A recent classroom session was attended by 10 students.

One of them, Ms Otgoutugs Ochir, a 46-year-old housewife originally from Mongolia, said she hopes to earn enough money to buy an apartment. But she also professes patriotism as a motive.

"If the number of those who make money illegally declines, my kids can live in a better environment," she said.

FLORAL DISPLAYS

An official with the government's Anti-Corruption and Civil Rights Committee said citizens reporting violations should provide detailed evidence.

"Anyone reporting should submit a paper document with his or her name on it. A single photo is difficult to build a case with," said the official, who declined to be named because he is not authorized to speak to media.

The weddings the two students staked out did not feature the congratulatory floral displays that are standard at such occasions. One of the students, Song Byung Soo, 60, saw that as a pre-emptive measure.

"Things have already changed lot," said Mr Song, who is looking to supplement the income he earns working for a company that sells auto parts but does not expect to hit the jackpot.

"I was hesitant because I have to hurt someone by doing this, but after the training, I think it is alright. If ran-parazzi can make our society clean without special favours or corruption, I think it is a good thing after all," he said.