OMAHA — Billionaire Warren Buffett is auctioning off a high-tech signed portrait of himself to raise money for one of his favorite charities, and the bidding has already topped $30,000.

Warren and Susan Buffett at their home at 5202 Underwood Ave. in 1956. The family was “back in Omaha and ready for a picnic,” The World-Herald reported. Susie was 2½, and Howard was 17 months. Warren ...