John Maloof first discovered the work of Vivian Maier in 2007, when he bought a box of her negatives at a Chicago auction house. Maloof was planning on using the photos to illustrate projects of his own, but soon enough recognized something special about the works he’d acquired.

“I didn’t buy them because I thought they were good work—I thought they would work for my book,” Maloof says now. “There was something that could have been done with them even if they didn’t work.”

But they did. In the years since Maloof bought that first box, Maier—a Chicago and New York nanny who took photos as a hobby and died in 2009—has been heralded as a genius and one of the first-ever street photographers. Her work, never seen during her lifetime, has been exhibited in galleries around the world and on March 28 a Maloof-directed film, Finding Vivian Maier chronicling his search to discover the true identity of the complex, compelling photographer, will be released.

Below, Maloof explains what makes three Maier images—out of his collection of close to 100,000—stand out to him.

“This is the elevated subway platform in Chicago. When we see color images like this, it’s refreshing because it’s more contemporary among [Maier’s] classic body of work. This shows off her eye for color and capturing a special moment.”

“I think this couple is arguing. It’s an interesting scene because Vivian sees the not-so-perfect moments in life in addition to the more polished and romantic scenes. This also speaks to what would interest her because of her own issues with men. This is a personal photo for her, an issue she’d take an interest in.”

“This is Vivian in the hat, and the girl on the right is one of the children she was a nanny for. That girl is also in the film. Vivian would do these self-portraits where she and some of the children are in the frame. She was documenting herself, often times in mirrors she’d find in the garbage or reflections in windows. There’s a whole book of self-portraits we just put out—Vivian Maier: Self-Portraits—because we thought those were really a strong body of her work. This is one I think is especially great.”

Finding Vivian Maier releases March 28; check here for screening info, and watch a trailer below:

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