[Sangetsu]

It's for the protection of the guests and customers, and also for liability purposes, though luckily Japan is not as litigious as America.

Recent high profile cases of people flipping out and going on killing/maiming rampages (remember the truck driving knife wielding man in Akihabara a few months ago?) has caused a surge in businesses purchasing camera equipment. It's amazing how many crimes, accidents, or general absurdities are caught on surveillance cameras.

People in Japan are generally not offended by nudity. Many public bathrooms are very public, with no doors, and most onsens are not that private either, with passers by usually being able to see the bathers. I remember taking a cable car to an onsen last summer and seeing both the mens and womens baths, both crowded with naked bathers.

Don't sweat about the cameras unless you and a lady friend have reserved a bath for the both of you, and are worried about becoming unknowing internet porno stars.