Gritty and Graffitied: Street art with photographer Martha Cooper

(CNN)Over the past four decades, New York-based photojournalist Martha Cooper has prolifically documented the rise of street art and graffiti -- capturing its shift from an underground subculture to a globally celebrated art form.

Cooper's first exposure to the world of street art and graffiti began in the late 70's, while she was working on assignment for The New York Post. She would often take photos of people and children around the city for feature stories.
    During one of these photo shoots, she met a young graffiti artist known as HE3, who introduced her to tags, or graffiti stylized artist signatures. HE3 also introduced Cooper to legendary graffiti artists of the time, including Dondi and Blade.
    Cooper became fascinated by the secret underground subculture that these graffiti artists had created in New York. At night, she would visit subway yards to document them at work.
    At 72, Cooper shows no signs of slowing down, and is still out photographing the world, continuing to capture street artists and their work.
    She points to "GIF-iti" by INSA and "Yarn Bombing" by Olek as examples of contemporary creatives pushing the boundaries of art.
    INSA's "Gif-iti" project (pictured left) involves painting and re-painting a wall, and then layers photos of the process to create a moving image.
    Olek's "Yarn Bombing" project (pictured below) swaps out spray cans for yarn, and involves using the process of crochet to create unconventional street art.
    Cooper will soon release the 3rd edition of "Subway Art" - a book that documents the rise of street and graffiti culture in New York City and features rare vintage photos by Cooper.
    Other noted works by Cooper include "Going Postal," which showcases a compilation of stickers, and "Tag Town" which offers an up close look at some of New York's most prolific tags.
    She is also currently gearing up for an exhibition entitled "Kids" - which shows a rare side of New York City's youth during the 1970s.
    The gallery above features Cooper's photos and conversations about her work, travels, and the evolving world of street art.