If she is younger yes it is true it is not a good Idea for her to be with out supervision in a park , if there is a group of her friends present she needs to have the unwanted touch and semi / full strangers talk. I would say every time this guy takes pics report it to the police even if it is after the fact. Sooner or later a officer may have the nerve to tell him that it appears he could be stalking ( as if he might be viewed by police as ped) that may be enough to get him to cease his poor choices.