In October Mr Xi met Ms Park again, in Indonesia, and urged that the two move forward on a bilateral free-trade agreement.Japanese officials have responded by calling Ahn a criminal.
Outside the mainstream is Ahn Chul-soo, a software entrepreneur and philanthropist who has not said he will run, but is popular among young people tired of South Korea's two-party status quo.
"If the benefit a spammer is getting from obtaining an e-mail account is less than $3 per 1,000, then CAPTCHA is doing a perfect job," says Dr von Ahn.
But first, there is the not insignificant matter of Mr Ahn.
Korean-American peace activist Ahn says that border crossing has a symbolic value for the group who hope their march will help "break the impasse and stalemate" between the two countries who've technically been at war since 1953.
This week China rejected criticism from Japan of a monument unveiled on January 19th in its northern city of Harbin to Ahn Jung-geun, a Korean nationalist executed by Japan in 1910 after he had carried out an assassination in the city.
Japan regards Ahn, who killed Hirobumi Ito, Japan's colonial governor in Korea, as a "terrorist".
So Mr Oh had to go.Now he is out of the race, Mr Ahn has thrown his weight behind another independent, Park Won-soon, a social reformer.
The ReCAPTCHA team has a member whose sole job is to break the system, says Dr von Ahn, and so far he has been unsuccessful.
He defended China's decision to press ahead with the statue.This will not be the first tribute to Ahn in China.
He combines an anti-chaebol message with a strong dose of progressivism.If both Mr Moon and Mr Ahn stay in the race, they will split the progressives' vote, handing easy victory to Ms Park.
