Whatever the couple is doing is their own business unless its hurting someone, since this isn't the case in this scenario, what the photographer and any spectator doing the peeping is invading people's privacy and while there's no privacy laws here it is ethically wrong. How would you like it if someone is constantly looking into your bathroom and photographing you as you shower?
EMm. Till now. Confirm is indecent exposure is in the wrong.
The photographer is no wrong as he is wrong if he shoot others in compromised positions / situations.
However, the indecent exposure already defined the situation. Thus, confirm the couple is in the wrong.