SAN FRANCISCO (Reuters) - Facebook is adding tools to make it easier for users to report so-called "revenge porn" and to automatically prevent the images from being shared again once they have been banned, the company said.

"Revenge porn" refers to the sharing of sexually explicit images on the internet, without the consent of the people depicted in the pictures, in order to extort or humiliate them. The practice disproportionately affects women, who are sometimes targeted by former partners.

Facebook has been sued in the United States and elsewhere by people who said it should have done more to prevent the practice. The company in 2015 made clear that images "shared in revenge" were forbidden, and users have long had the ability to report posts as violating the terms of service.

Beginning on Wednesday, users of the world's largest social network should see an option to report a picture as inappropriate specifically because it is a "nude photo of me," Facebook said in a statement.

The company also said it was launching an automated process to prevent the repeat sharing of banned images. Photo-matching software will keep the pictures off the core Facebook network as well as off its Instagram and Messenger services, it said.

Users who share "revenge porn" may see their accounts disabled, the company said.

Facing criticism, the company last year met representatives from more than 150 women's safety organizations and decided it needed to do more, Antigone Davis, global head of safety at Facebook, said in a phone interview.

A specially trained group of Facebook employees will provide human review of each reported image, Davis said.

The process to prevent repeat sharing requires Facebook to retain the banned pictures in a database, although the images are blurred and only a small number of employees have access to the database, the company said.

Prosecutors and lawmakers have also sought ways to prevent the spread of "revenge porn," seeking additional penalties for a practice that they said has ruined careers and families and even led to suicide.

(Reporting by David Ingram; Editing by Andrew Hay)