Like many Instagram users, Natalie Landsberg, Gillian Presto and Emily Morse frequently posted photos of what they were eating.

But as their joint account @New_Fork_City took off, they found themselves with nearly 500,000 followers, and soon, free restaurant meals, gigs “curating” food for a music festival and an offer to create their own cookie-dough flavor.

The three 19-year-olds, who started the account in high school, are now in college, and their modest Instagram earnings aren’t footing their tuition bills yet. But their parents spent almost $15,000 to trademark the New_Fork_City name and create a limited liability company, “so down the road, if there is an opportunity to figure out a financial business model, the company is established,” said Ms. Presto’s father, Michael Presto.

Meet the professional food Instagrammers, courted by restaurants for their six-figure followings and stylish, sometimes over-the-top photography. Some have turned their accounts into full- or part-time professions, earning up to $350 for posting a flattering image, while others have parlayed their social-media savvy into free meals or public-relations jobs.

“There are people who decide on where they want to go out to eat by their Instagram feed, and that’s a fact that we in the hospitality industry just cannot ignore,” said Helen Zhang, director of media strategy at LFB Media Group, a public-relations agency that works with such restaurants as the Stanton Social and Casa Nonna.

Olivia Young, brand and communications director for the Altamarea Group, which operates restaurants such as Vaucluse and Osteria Morini, said the company has begun inviting some Instagram users for meals and plans to pay some to post photos.