https://www.theregister.co.uk/2017/11/08/facebook_wants_nude_photos/

Facebook has begun conducting a pilot where it solicits intimate photographs of women – and it will soon offer the service in the United Kingdom. Anxious exes who fear their former partner is set on revenge porn will be urged to upload photographs of themselves nude.

A hash of the nude image is created and passed along to Facebook's AI image-matching systems. Subsequent unauthorised attempts to post on one of Facebook's services (including Instagram), the image are then blocked.