I think of these images as a ticking time bomb.
Suppose I build a nuclear bomb out of spare junk and keep it in my garden shed. I think I know it won't go off and I think my garden shed is secure because I bought a $50.00 lock instead of a $2.00 cheapie. Instead somebody breaks into my shed wanting to steal my lawnmower to pawn it for drug money and sets off my bomb instead.

Oops.
I do computer and network security as part of my living. In a few minutes I'm going to make a phone call and chew somebody a new asshole for a very similar situation.
The girl and boy in question may think their computers are secure (I'll bet they're running Windows. Yes, I'll stop giggling now) and they may think their network connection is secure. It ain't. Unless they're going to extraordinary lengths (which is probably beyond their level of expertise) to establish a secure connection (which even I won't swear in court is possible) I can snoop that picture just fine, thank you.
If they've managed to catch themselves a virus or trojan, it could be rummaging around through their hard drives looking for interesting pictures. It could even have an algorithm to pick out the jpg's with lots of pink and pass them along or just broadcast them to the world for the hell of it. To quote Alfred "some men just want to watch the world burn".
How do I know all this? I'm the one who gets to sit on the intertubes watching the packets flow in, figure out which employee is violating the corporate computer use policy, break into his computer, see what disgusting images he's managed to download (one manager had nearly a gigabyte of anime porn) and watch his face turn all sorts of interesting colours (red to white to "I'm gonna puke" green) as I give "the speech".
Some of the worst images are scans of photographs taken decades before digital cameras. It may have started out in the 50's as some hubby shooting a naughty picture of his wife for his own use, but now it's crossing my corporate network, sitting on my expensive file server and wasting my time when I'd rather be doing useful work.
Should I be building a bomb in my back yard? (Agent Mike, piss off - it's an analogy)
To quote Spiderman, "with great power comes great responsibility" (gee, two movie quotes in one post).
If I have the power (ie. intelligence, mechanical expertise) to build a bomb, and that's what I want to do to get my rocks off, I have the responsibility to go work someplace where that's what you do for a living. Failing that, I have the responsibility to either not do it or take my lumps if things go awry.
If little miss chickie has "the power to cloud mens' minds" (oh crap, that's three) by flashing her titties over the intertubes, she (and her recipient if he put her up to it) need to take their lumps as well.
Incidentally, "Romeo and Juliet" laws have no precedent here. If the happy couple were flashing each other out their adjacent bedroom windows and visible from the street, the same would apply.