Facebook, the world’s largest social network and the largest photo-sharing site on the Internet, has taken a big step in the fight against child pornography by joining Microsoft in partnership with National Center for Missing and Exploited Children (NCMEC) on PhotoDNA program. Facebook will be the first company besides Microsoft to utilize PhotoDNA technology, an image-matching technology developed by the Redmond-based giant company and freely licensed to NCMEC for use in a program to stop the distribution of known images of child sexual abuse online.

PhotoDNA has the power to quickly and accurately identify child porn images among Facebook’s billions of files shared online. In just one month, Facebook’s services host more than 30 billion pieces of shared content, including photos, web links, news stories, blog posts and more. Identifying images of child pornography in a sea of content like that is a disheartening task, but PhotoDNA is helping to find the needle in the haystack.

PhotoDNA works by breaking images into different blocks, using a precise set of measurements to find illegal photos even if they’ve been resized, cropped or modified. Tests on Microsoft properties showed it accurately identifies images 99.7 percent of the time and sets off a false alarm only once in every 2 billion images.

“We’ve found it to be a very powerful tool in identifying these images,” Chris Sonderby, Facebook’s assistant general counsel said.

Before utilizing PhotoDNA, Facebook relied primarily on abuse reports from its users, reviewed by trained employees, to find and eliminate offensive images. But with this effective tool, it can keep child pornography from making it onto its site in the first place.

“Our hope and belief is that Facebook will be just the first of many companies to use what has proven to be highly effective technology,” said Ernie Allen, chief executive of the National Center for Missing & Exploited Children. “Online services are going to become a hostile place for child pornographers and pedophiles.”