well, all you really need is to sound intimidating, which works a lot of the time. Haha, just bear with me here. Why don’t you contact them threatening legal action if they don’t remove the said pictures. This usually works as most people want to avoid legal trouble. If they still refuse, then start to actually find out what you can do legally, do some research on copyright, privacy and harassment laws.

Good luck with that.

As long as they are not using it for commercial purposes, there’s not much you can do about it legally. You can either ask nicely or deliver an empty threat, whichever you think is more likely to work.