THE name Marty Hyman may mean nothing to you. But if you, your children or grandchildren have gone to private schools in and around Manhattan over the last 30 years, chances are you’ve either smiled for Mr. Hyman or written him a check.

That’s because with an account list of 500 — including Dalton, Chapin, Hewitt, Riverdale, St. David’s, Grace Church and the 92nd Street Y, as well as public schools and camps in the metropolitan area — Mr. Hyman, 67, is practically the Irving Penn of the preschool and preteen set.

A few Fridays ago, there he was at the Windmill Montessori School in Brooklyn, taking candid pictures. Like an eager politician on a campaign swing, Mr. Hyman, known in certain circles as the picture man, made his way through Windmill’s two buildings seeking not votes, but smiles.

“I just saw you kids downstairs — you were eating yogurt,” he said, announcing himself to a group of 7- and 8-year-olds.

“We were doing yoga, not eating yogurt,” corrected Brendan, who laughed obligingly as Mr. Hyman peered through the viewfinder of his Canon digital SLR and snapped away.

“What a face — look at that face,” Mr. Hyman said, taking his grin-winning approach to 8-year-old Brian.

With his graying beard and bad back — a hazard of the profession — Mr. Hyman is something of a legend among school administrators. He was greeted by Liza Herzberg, Windmill’s director, like a favorite family member. But it might be more accurate to think of Mr. Hyman and others in his business as members of an endangered species.

About 5 to 10 years ago, class photos and individual student portraits were reflexive purchases for parents. Those 4-by-6 and 8-by-10 prints were the visual equivalents of the notches made on door frames to show how much Junior had grown since last year. Now, more parents are snapping their own digital pictures and declining the products of the pros. It’s a situation akin to the disappearance of the formal engagement and wedding portraits, courtesy of Bachrach, that were once a staple of newspaper society pages.

Mr. Hyman, who grew up in Brooklyn, began taking pictures as a teenager when his uncle gave him an old Voigtländer. Later on, after teaching junior high school for a decade, he wearied of the bureaucracy and turned his summer job photographing children at a Westchester day camp into a full-time job.

He has a couple of plush toys and shticks that have served him well. Way back when “Sesame Street” became popular, he and the 10 photographers on his staff started carrying around Cookie Monster dolls, then added a purple dinosaur when Barney was in its ascendancy. Those props, periodically replaced, still work well. “The character’s name should have an ‘e’ sound so the kids go into a smile when they say it,” Mr. Hyman said.

He also engages the children by insisting he can guess a name with just the clue of a first initial.

“You do that for a few minutes, and they’re your friends,” he said. “Of course, these days everyone is called Madison.”

The highest profit per shutter click in the school photography business is the high school senior picture, “but we just never got into it,” Mr. Hyman said.

“You don’t have to be a genius to be able to take a 16-year-old girl who’s eager to have her picture taken and tell her how to sit, tip her head a certain way and give a nice little smile,” he continued. “But when you got a 2 1/2-year-old, a 5-year-old, it’s a whole other set of skills. If you can do young kids, you can do any kids.”

Mr. Hyman’s main rival is Irvin Simon Photography, which is based in Elmont, N.Y., and has 1,000 accounts, according to Steve Miller, 39, whose father bought the company in 1980. These include New York Public Schools 3, 6, 87, 89, 158 and 234 as well as many summer camps, Mr. Miller said.

Highpoint Pictures, another competitor, has a broader geographic reach — its clients include the upper division of Horace Mann and independent schools as far away as Noble and Greenough in Dedham, Mass. Then, of course, there are those other pesky competitors: shutterbug parents.

“They take pictures of their kids on their camera phones,” Mr. Hyman said. “They take them on their digital cameras and print them on their printers or get them from Costco for 13 cents a copy. They’re not good, but they’re good enough. I lost at least one account at a school that farmed out the photography to a mother in the PTA.”

The statistics back him up. According to the Photo Marketing Association, 20.8 percent of all American households bought K-11 school portraits in 2008, the most recent year for which data is available, spending an estimated $920 million. In 2007, it was more than a quarter of households spending $1.127 billion.

To hold on to certain clients, Mr. Hyman said, he has sometimes been compelled to provide free photo stickers for school ID cards and free head-shot images for school databases. At least once — at a parent’s request — he Photoshopped an absent child into the class picture.

“Other photographers have solicited our business, but I see no need to switch,” said Jan Barnett, an administrator at the Dalton School. “The children love him, the teachers love working with him, the product is beautiful. Rarely is there a blink in the pictures.”

Ms. Herzberg of Windmill Montessori agreed. “Marty takes amazing pictures,” she said. “You can tell who the kids are and what they’re about from the images.”

At Windmill Montessori, Mr. Hyman headed into a class where 4-year-old Elliot was busily cutting construction paper. “What are you making, cutie pie?” he asked as he snapped off a few shots and then worked the room. “Look at these great puppets!” he said with enthusiasm, adding, “Don’t look at the camera, just keep doing your work.”

Sophia, who is 4, posed by the pink cage holding the class hamster, Bella. “The hamster goes up and down every day,” she earnestly informed Mr. Hyman.

Mr. Hyman’s definition of candid photography was sometimes a bit fluid. “Sit down there and grab a book and make believe you’re reading,” he told Hannah, a 4-year-old with pigtails, who obediently took a book from a shelf and sat on a small rug. “Where’s your smile?” he asked teasingly. “Where’s that smile?”

“You’re so silly,” Hannah said.

He moved on to his last stop of the morning, Stepping Stones, a room of 2- and 3-year-olds.

“Who’s that guy?” Mr. Hyman asked 2 1/2-year-old Ryan, showing the boy an image of himself in the viewfinder.

Then: “I’ve got an idea,” he said. ”When I count to three, I want you all to say ‘Dinosaur!’ ”

Mr. Hyman is selling tradition and continuity in the form of a familiar tableau: three rows of children with gap-toothed frozen grins, teachers smiling in the back row. It’s a commodity that fluctuates in value. These days for Mr. Hyman, a respectable sale is $45 to $50.

“When kids are little, they’re the cutest things,” he said. “When they’ve been driving you crazy for a few years, you’re not going to do the $49.95 package. You buy the class picture for $10 and say ‘Get away from me.’ ”