At dusk on New Year's Eve, Erika Gunderson got into a taxi in New York City and entered a digital-age mystery.

Sitting on the back seat was a nice Canon digital camera. Gunderson asked the driver which previous passenger might have left it, but the cabbie didn't seem to care. So Gunderson brought it home and showed it to her fiance, Brian Ascher. They decided that the only right thing to do was to find the owner.

But how? The only clues were the pictures on the camera: typical tourist snapshots, complete with a visit to the Statue of Liberty. How could they find a stranger among the huddled masses?

Gunderson is busy in finance for Bear Stearns Cos., so the detective quest fell to Ascher, a 26-year-old law student at New York University. He was on winter break and eager to put off writing a paper about climate change treaties.

He checked whether anyone had reported a matching missing camera to the city's Taxi and Limousine Commission. No dice. He placed ads in lost-and-found sections of Craigslist but got just one response — from a couple in Brazil who had lost a camera in a cab on Oct. 12, not Dec. 31.

"I guess they thought their camera had been riding around in a taxi for two months," Ascher recalls now, chuckling at the notion that such a thing would be possible in New York.

LOOKING AT THE CLUES

The 350 pictures and two videos on the camera showed several adults, an older woman and three children. Half put them at New York sites such as the Empire State Building. The other half had the group enjoying warm weather and frolicking at kid-friendly theme parks.

Ascher easily pinpointed Florida. The group had stood in front of a sign indicating Clearwater, Fla., and posed at Bob Heilman's Beachcomber Restaurant there.

They also took a pirate-themed boat ride where the kids got mustaches painted on their faces. Ascher zoomed in on the group to see name tags on their shirts. He spotted an Alan, an Eileen, a male Noel and a female Noelle, plus a Ciarnan. Under their names was written "IRE."

When Ascher checked the videos, he saw nothing telling, just the children dancing and swimming. But in the background, he heard Irish accents.

OK, Ascher figured, the camera's owner is from Ireland.

Ascher called Canon's Ireland division to see if anyone had registered the $500 camera's serial number. No such luck. He posted ads on Irish Web sites. Nothing.

He checked the date stamp on the photos from Bob Heilman's and called to inquire whether anyone remembered serving a big Irish group that day. Without the diners' last names, there was no way to check. It's a nice thing you're trying, the manager told Ascher, but you probably just found yourself a new camera.

Enter some fresh eyes. Ascher's mother, Nancy, and sister, Emily Rann, scoured the pictures for clues he might have missed. Nancy was particularly confident, having reunited people with their lost belongings before. She once found a California woman's wallet in a cab in Florence, Italy, and spent all day on her trail before making a handover at an American Express office.

"I thought, with all this data in the camera, there's no way we're not going to get it back to them," Nancy Ascher says now. "I was hoping it wasn't going to take a trip to Ireland, flashing their pictures everywhere."

Ascher's mother and his sister noticed that one of the pictures showed a doorman helping someone into a New York taxi. Zooming tight on the doorman's uniform, they made out the logo of the Radisson Hotel.

After several phone calls and a visit to the hotel to show the pictures around, Nancy Ascher persuaded an employee to search the Radisson's guest records by first name and country of residence. Indeed, a Noel from Ireland had stayed there on the date stamped on the photo. Nancy Ascher charmed the hotel employee into sharing the guest's e-mail address.

Wonderful.

Except that when Noel responded to Brian Ascher, he said he hadn't lost a camera.

ONE SMALL DETAIL

By now, school was resuming, and Ascher was prepared to give the camera to his mom so she could take over. She had figured out the name of the Florida pirate-boat cruise and was trying to reach its operator.

But first Ascher took a final look at the photographs.

He pored over some from Dec. 30 that didn't include the children. The photos showed signs for bars in Manhattan's East Village: The Thirsty Scholar, Telephone Bar, Burp Castle. There also were multiple interior shots of a tavern, but they didn't seem to fit with what Ascher knew of those other three bars.

Then he stopped on another picture, showing two people outside an apartment building. Seemingly accidentally included in the picture was something Ascher had missed the first time: an awning in the background that read "Standings." Aha! Standings is a bar next to Burp Castle. Ascher checked its Web site, and the interior matched the pictures on the camera.

Ascher found Standings' owner, who reached the bartender who had worked Dec. 30. Yes, he recalled an Irish group — because one of the women was a big tipper and said she worked at another New York City bar, Playwrights. The Standings bartender called Playwrights to ask which employees had been in his bar.

Ascher soon got an e-mail from a woman named Sarah Casey, whose sister, Jeanette, works at Playwrights. Suddenly everything Ascher had seen on the camera came to life.

The Caseys recently had hosted relatives and friends from Ireland. The group included their friend Alan Murphy, who had journeyed to Florida with family before heading to New York, where the clan stayed at the Radisson. (Their Noel was not the Noel whom Ascher e-mailed.) Murphy ended the trip kicking himself for leaving his camera in a cab in the twilight on New Year's Eve.

Sarah Casey agreed to send it to him. It didn't go to Ireland but to Sydney, Australia, where Murphy lives now.

Murphy, an insurance underwriter, had been devastated to lose the pictures from a trip he had planned for years. It was Jan. 10 — his 34th birthday — when he heard he would be getting the photos back. "I was over the moon," he says now. "Best present ever."

"I owe you one," he wrote to Ascher. "It's good to know there are some honest people left in the world."