The story of the street photographer Vivian Maier has always been tangled — she worked much of her life as a nanny, keeping her artistic life a secret, and only after she died in 2009, at the age of 83, nearly penniless and with no family, were her pictures declared to be among the most remarkable of the 20th century. Now a court case in Chicago seeking to name a previously unknown heir is threatening to tie her legacy in knots and could prevent her work from being seen again for years.

The case was filed in June by a former commercial photographer and lawyer, David C. Deal, who said he became fascinated with Maier’s life in law school and took it upon himself to try to track down an heir. He did so, he said, because he was upset that prints of her work — from more than 100,000 negatives found in a storage locker at an auction, containing images now possibly worth millions of dollars — were being sold by people who came to own the negatives but had no family connection to Maier, who spent most of her childhood in France and worked in Chicago, where she died.

“I was, for 20 years, a commercial freelance photographer, and then became a lawyer,” said Mr. Deal, who practices in Orange, Va. “And, as a photographer and an attorney, the situation bothered me, so I decided to do some research on it.”

Chief among the owners of Maier’s work is John Maloof, a former real estate agent in Chicago who bought tens of thousands of the negatives for less than $400 in 2007 and has spent years tending and promoting her work through commercial galleries, museum exhibitions, books and a recent documentary, “Finding Vivian Maier,” that he helped direct. Mr. Maloof hired genealogists to find heirs to Maier in France and eventually paid an undisclosed amount for the rights to her work to a man named Sylvain Jaussaud, whom experts identified as her closest relative, a first cousin once removed.