The "guerrilla girls" who changed the art world

In 1985 a group of anonymous female artists in New York began dressing up in gorilla masks and fly-posting around the city's museums and galleries.

It was part of a campaign to demand greater representation for women and ethnic minorities in the art world.

Two of the activists, who call themselves "Frida Kahlo" and "Käthe Kollwitz" spoke to Witness History about their work.