Photographer Janette Beckman took photos of young up-and-coming punk bands in London in the 1970s. A decade later, she moved to New York at the dawn of hip-hop, and photographed bands like Run DMC, the Beastie Boys, and LL Cool J. She teamed up with Cey Adams, who started as a graffiti artist, then became Creative Director at Def Jam Records to create a book and exhibition called “The Mash Up.”