OMAHA (REUTERS) - A signed portrait of Mr Warren Buffett fetched US$75,100 (S$105,000) at auction, with proceeds to benefit a hometown charity that the billionaire investor has long supported.

The auction concluded on eBay on Tuesday night, Mr Buffett's 92nd birthday. The winner was not immediately identified.

Created by Motiva Art, the high-tech portrait features rows of letters that light up to spell quotations attributed to Mr Buffett, such as "Women make me optimistic about America".

It was displayed in April at the annual shareholder weekend of Omaha, Nebraska-based Berkshire Hathaway, where Mr Buffett is chairman.

Proceeds will benefit Girls Inc of Omaha, which offers educational and recreational opportunities to girls from lower-income neighbourhoods.

Mr Buffett's daughter Susie has long worked with the group's national organisation, which serves more than 350 cities in the United States and Canada.

While substantial, the US$75,100 top bid fell far short of the US$19 million that someone agreed to pay at auction in June for a private lunch with Mr Buffett. Proceeds from that auction benefited San Francisco's Glide, which helps the poor, the homeless and substance abusers.

Mr Buffett has auctioned several items to benefit Girls Inc. Another portrait of him painted at the 2008 Berkshire shareholder weekend sold for US$100,000. It was moved five years later to the University of Nebraska at Omaha's business school.

In 2015, Mr Buffett auctioned his 2006 Cadillac DTS sedan, with his autograph on the dashboard, for US$122,500. And in 2018, Girls Inc received about US$2.2 million after Mr Buffett won a bet that a Standard & Poor's 500 index fund would outperform a basket of hedge funds over 10 years.

Mr Buffett is giving away nearly all of his fortune. He was worth US$99.4 billion on Tuesday, Forbes magazine said, despite having donated more than half of his Berkshire stock since 2006.