On a quiet afternoon in late July, in a shady yard on a quiet side street, 150-pound Chaos perched on a limb about 5 feet off the ground.

“Gooood,” cooed Carlene White of the Service Dog Project Inc. “Stay.”

Photographer William Huber of Newton moved his tripod a couple of feet, refocused, and resumed snapping pictures. Chaos belied her name by obligingly looking toward the lens for a moment. Then she began to glance around to see if there were any more of the hunks of roast beef used to lure her up the ramp into the huge tree.

“Stay,” insisted White. She is gray-haired and petite and bespectacled, but her command voice is not to be taken lightly. “Stay. Stay. STAY!”

Chaos complied, posing for another minute or two on the branch of the giant tree. Then White and others moved in with a ramp and more beef, and Chaos returned to her spot on the lawn with two other Great Danes, Bentley and Bailey, who also took turns in the tree.

“We got that shot in 20 minutes,” Huber announced. “You know, that’s a record.”

“OK,” someone else said, “Bring in the cat.”

The photo session was for a calendar benefiting the Service Dog Project. The dog and cat would meet later in Huber’s computer. But as funny and beautiful as the pictures will be, there’s no way they can match the impact of the dogs themselves.

Most people are familiar with guide dogs for the visually impaired and other types of helper animals for those with sensory or mobility challenges. But the Great Danes raised and trained by White on her Ipswich farm have a mission specific to their size. They help people with balance issues stay upright.

It’s literally a “lean on me” situation for people with Parkinson’s disease or multiple sclerosis, a stroke, or traumatic brain injury. Half of the 42 dogs donated by the organization since 2003 have gone to injured military combat veterans, who get preference.

Wenham resident Gay Roland suffered a non-life-threatening trauma, a fall that left her with several broken bones in her ankle and foot. But she is unable to walk upright even years later, dependent on her husband or a cane or the nearest wall for balance.

“It was debilitating. I didn’t feel safe walking by myself,” she said. “Many times I would find myself almost tipping over walking down a corridor. It was embarrassing, I’ll be honest.”

Still, when a snowstorm damaged a training arena at White’s farm, Roland and her husband answered a call in the local newspaper for volunteers to give the dogs some extra attention. After a few visits, Roland said, White approached her. “She said, ‘I’m so tired of seeing you with that mmm-mmm cane, would you like a dog to help you walk?’”

Soon after, Roland was paired with HeyDawg, a mostly black, yard-tall, 140-pound Great Dane to begin their training. They’ve been together about a year now, and he walks her through the supermarket, around the yard, and last week even down a busy Salem sidewalk to an appointment. Often he wears a harness identifying him as a service dog.

“Having HeyDawg, I’m able to walk wherever I want to,” Roland said. “He has given me the ability to be independent.”

For three decades, White ran Animal Episodes, a company she founded that provided animal actors to New England TV and movie production, advertising, and other media and entertainment. A decade or so ago, she turned her attention and training talents to service dogs.

“I got old,” she said after the photo shoot. “I’m 74, you know. I just got tired of carrying rabbits around Harvard Square and chasing pigs down Storrow Drive.”

She started to tell a story about TV sportscaster Bob Lobel and a string of donkeys wearing fake reindeer antlers, then said with a wry smile that it was too long.

Her career change also had to do with her father, who had Parkinson’s, and a close friend with MS. She turned her dog-training skills and a sudden surfeit of Great Dane puppies — things happen — to a new purpose.

“It works!” White said. “I have taken people who come up my driveway in a wheelchair and I’ve stood them up and said, ‘Take ahold of this dog and walk.’ And they walk. They haven’t walked in years by themselves.

“You can’t really balance with a walker or a cane, because you go over backwards. You don’t go over backwards if you’ve got a 150-pound dog on handles. I don’t know what I’m doing, if the truth be told. It just started. It’s unbelievable, actually. We’ve got a lot of applicants now.”