Well, this one is defiantly questionable. No naughty parts are showing, there's nothing really "seductive" about the picture, and It's unclear if the picture represents any sexuality. Personally I think you'll find more offensive pictures at an art gallery. Or a museum with renaissance artwork. But you can't really mark it as "safe" because of the nudity. Hmm...

You can. It's completely casual nudity, with not a trace of anything sexual about it.