How flash photography put a spotlight on New York’s rampant poverty in the late 1800s, catalyzing the demolition of the city’s biggest slums

• Danish photographer Jacob Riis captured the inhumane conditions of New York’s slums in his book, “How the Other Half Lives.”

• He documented the poverty previously hidden in darkness using a magnesium powder to produce a flash.
• His work led to changes in the city and prompted then-Police Commissioner Theodore Roosevelt into action.

In the 19th century, New York City was filled with more than 1 million immigrants living in poverty.

Despite the vast number, they were easy to ignore because they lived in windowless tenements and the underbelly committed crimes down dark alleys.

But the world caught on when Jacob August Riis, a Danish journalist and photographer, started documenting poverty using a recently invented flash magnesium powder. He later released a photojournalism book, “How the Other Half Lives: Studies among the Tenements of New York.” The book raised awareness about poverty in New York and prompted officials to take action.

Here are some of the photos that changed New York City — and America — forever.