Twitter recently announced that it was changing its policy related to violent images and videos within its platform. 

The move comes as the loved ones of kidnapped American photojournalist James Foley have been asking people not to share images or video of his beheading at the hands of extremists. Last week, Zelda Williams quit Twitter after people harassed her with offensive images of her father Robin Williams following his death.

YouTube, Facebook and Twitter and many more of the places we live online have dealt with similar challenges. But there’s an interesting layer to this.

Even if we don’t share images of violence, we sometimes still promote them in the view of the algorithms that measure our engagement.

Karen North, professor of social media and psychology at USC Annenberg, thinks a lot about how content spreads on the web.

Click the media player above to hear Karen North in conversation with Marketplace Tech host Ben Johnson.