Quote from @Carlton B.:
First I would ask him to leave letting him know my intent to make his actions public. If he did not leave I would call the police and let him know I'm calling the police even if its not illegal still have it on record. Next i would let everyone he knows understand he is a pervert. Basically try to embarrass him to the point he wants to leave.
Is there a fine line there of slander/deformation? Not saying there is or isn't was just the first thing that came to mind reading the post. Personally I like the idea, just unsure of the legality of it haha.
As far as calling the police generally around me the police hate and sometimes flat out refuse to get involved in tenant/LL conflicts and tell you it is a civil matter and unless a criminal law has been violated there is nothing they can do. The most I have seen them do in similar situations is show up to allow access and deter any conflict during such times. I am not an attorney but I do not believe the tenant has done anything criminal even by sending inappropriate photos, that I think would only rise to the level of Sexual Harassment which I do not believe is criminal that is a civil matter until it becomes assault/battery.
You would maybe be able to get the police (if you get the right one) to go talk to and possibly scare him telling him to stop what he is doing.
*Disclaimer this is not a bash on police, I support law enforcement.