There are lots of pictures of naked people online. Millions probably. A visual effect that makes it look like someone is naked isn't that impressive, because there are naked people all over the place. The nudity aspect isn't the most precise description of what makes the bubbles effect interesting, it is the undressing aspect that makes it a interesting psychological/visual effect.
because if you are at 'work' or such environment that warrants the NSFW (Not Safe For Work) tag distinction and you click on a bubbled picture, it would give the illusion of viewing softcore pornography rather than, say, a typical bikini picture from a social networking site (which would arguably not be okay to view at work to being with).