Maggie Gyllenhaal and Sheryl Crow have united to help to expose human rights violations in the world, via video and digital media.
Witness is currently in its sixth year, and this year the organisation's gala was hosted by the British rock musician Peter Gabriel.
Gyllenhaal described how the use of video images can change the way people think:
"I was 8 or 9 years old when I saw Tiananmen Square. That man standing in front of that tank and risking his life for something he believed in. I had never seen anything like that before. It changed my life.
"Right now anyone can just pick up a camera and record something and put it online. And everyone will see it."
Nine time Grammy winner, Sheryl Crow, performed at the event but believes there are some disadvantages to using digital media to reach the masses: "I think that there are great things about it, and I think that there are dangerous things about it. I think the amount of misinformation that goes around is probably as prevalent as the amount of correct information.
"You just hope that people will use their ability to discern what's reality and what's untruth and what's truth."