Jacob Riis profoundly changed the image of poverty in New York City after he published his photographs in 1890. Photography was still in its infancy, so Riis actually had to invent a new method of lighting up the dark spaces in which the poor lived. His photos were so shocking that they actually brought about reforms that significantly improved the conditions of the working poor (mostly immigrants) living in New York City.
If you have not seen his photos, I would highly recommend doing so. They are shocking! I posted a few below. How The Other Half Lives, by Jacob Riis: