Can he do this?

Hi all! This might be odd, I know a man that posted a picture of a random woman’s ass (with jeans on). Not only did he take it without permission, he also posted it to Facebook like a dirty old man. I’m just wondering if any of you know if that is actually illegal in some way or not okay. I’m thinking of reporting it. He posted a second picture showing her whole backside also. She has no clue she’s being posted on his Facebook. Sorry if any of you get offended, I just find this so perverted and terrible.