Blac Chyna Sued Over Paparazzi Pic with Rob Kardashian and Cairo

Blac Chyna just got slapped with a lawsuit over a photo of herself, Rob Kardashian and her son ... which she posted but does NOT own ... according to the suit.

A photo agency -- FameFlynet -- is going after Chyna for the December 2016 shot showing her and Rob taking King Cairo out in Calabasas. According to the suit, the photo was legitimately licensed and posted by several websites on December 2.

The agency's beef is with Chyna for reposting the image from one of those websites on her Instagram page ... while stripping FameFlynet's credit. BC has since deleted the shot that included Rob -- maybe on account of the nasty breakup -- but she still has a pic of her and King from that day.

The agency wants Chyna to fork over all profits she made from posting the shot.