A spokesman for Richland County Sheriff Leon Lott, who is known for his tough stance on drugs, said Tuesday the department was investigating.

"Our narcotics division is reviewing the information that we have, and they're investigating what charges, if any, will be filed," said Lt. Chris Cowan, a spokesman for the agency.

The photo first shown in British tabloid News of the World on Sunday was snapped during a November party while Phelps was visiting the university, according to the paper.

Phelps, 23, and his team have not disputed the photo's accuracy. Phelps has issued a public apology, acknowledging "regrettable" behavior and "bad judgment" after the photo appeared.

One of Phelps' agents, Drew Johnson, said Tuesday authorities had not contacted the swimmer. "So we really can't speculate," he said.

Last fall, Phelps was introduced to large applause at South Carolina's football game with Arkansas. He met with players and visited with Gamecocks coach Steve Spurrier, who gave Phelps one of the ball coach's trademark visors.

Phelps also spoke at a university class on sports' role in society.

Where exactly the party occurred isn't clear. The university said its police have no evidence it was on campus, and city police said they won't pursue criminal charges unless more information comes forward.

The Richland County sheriff can pursue charges as long as the party was in the county, the spokesman said.

"The bottom line is, if he broke the law, and he did it in Richland County, he's going to be charged," Cowan said. "And there's no difference between Michael Phelps and several other people that we arrest for the same type of a charge everyday."

Under South Carolina law, possession of one ounce or less of marijuana is a misdemeanor that carries a fine up to $200 and 30 days in jail for the first offense. Possession of paraphernalia is a $500 fine.

The Richland County sheriff has long sought to fight drug crimes. He rose from patrol officer to captain of the narcotics division in the early 1990s, after the television series "Miami Vice" made its splash.

Lott played the part well. He wore stylish suits and had long hair then. He drove a Porsche seized from a drug dealer and even worked undercover with federal agents in Florida.

Meanwhile, another of Phelps' big-name sponsors -- credit-payment processor Visa Inc. -- said Tuesday that it will continue to support him.

"We have spoken with Michael, and he has expressed regret for the situation, has committed to being accountable and improving his judgment in the future," the company said. "We intend to support him as he looks to move forward."

On Monday, sponsors including apparel company Speedo, luxury Swiss watchmaker Omega and sports beverage PureSport's maker Human Performance Labs also said they stand behind the athlete, even if they don't condone his behavior.

Some of Phelps' sponsors still weren't commenting Tuesday. A spokeswoman at Battle Creek, Mich.-based Kellogg Co. said the cereal maker declined to comment. The company put Phelps on boxes of its Frosted Flakes and Corn Flakes.

Information from The Associated Press was used in this report.