Who was Vivian Maier? The story of this eccentric woman with an incredible urge to photograph daily life on the streets of New York and Chicago is just as fascinating as her recently discovered snapshots. To those who asked what she did for a living, she'd say: "I'm a sort of spy." An exhibition in Berlin now explores the works of this prolific yet intriguingly elusive photographer.

Born in 1926 in New York from a French mother and an Austro-Hungarian father, she spent her childhood between Europe and the United States. In 1951, she settled in the US and became a nanny, working for different families over the next 40 years. One of the children she nannied would say of this spirited feminist: "She was like a real, live Mary Poppins."

She'd take the children she was caring for on countless day trips to bustling downtown New York and later to the seedy areas of Chicago and document the world around her. She also travelled alone to remote countries, from South America to the Middle East and Asia. The Rolleiflex she carried around her neck became her trademark, but nobody knew her work.

Extremely private, she always locked her room in her employers' homes. She kept the pictures she took to herself, accumulating over the years over 100,000 undeveloped negatives and series of homemade documentary films and audio recordings she had made, but also piles of newspaper clippings and found objects. These would all end up in storage rooms.

Towards the end of her life, Vivian Maier was too poor to pay the rent for this storage space and her photos were auctioned off. John Maloof, a real-estate agent with a passion for garage sales, bought a box packed with about 30,000 negatives for about 400 dollars in 2007. The amateur historian was trying to find pictures for a book on Chicago, but he did not manage to track down the photographer.

Even if Vivian Maier is now one of the most famous American street photographers, she had nothing to do with this recently acquired fame. She spent the last years of her life nearly penniless and was almost evicted from her cheap apartment. The Gensburg family, whom she used to work for in the 1970s, helped her out afterwards. She died in 2009 at the age of 83.

John Maloof happened to try to track her down again shortly after her death in 2009 and found her obituary on the Internet. It would help him further research her story and get in touch with some of the people who knew her. A discussion he posted on Flickr made the photos go viral. He started promoting her work, developing and scanning Vivian Maier's photographic legacy.

Maloof decided to make a documentary on his obsessive detective work, as he tried to find out "why a nanny would be taking all these pictures." The film "Finding Vivian Maier" won several awards and was nominated for Best Documentary Feature this year at the Oscars. Maier's story deviates from the usual narratives about artistic ambition, which makes it so fascinating.

Some criticize the way Maloof promotes his discovery in the film. A long-running legal dispute has been complicating the case. Maloof, one of the main owners Maier's work (along with Jeffrey Goldstein), had already settled with a French cousin to secure the copyright. But since 2014, the executor of her estate has been finding other possible heirs: 10 distant cousins were identified in June 2018.

The copyright issue may take years to resolve. The posthumous promotion of this very private woman's work also sparks debates in the art world. Still Vivian Maier's unique story should not overshadow the quality of her street photography, compared to the likes of Robert Frank and Diane Arbus. The exhibition at the Willy-Brandt-Haus in Berlin runs from September 25, 2018, through January 6, 2019.