As a rule of thumb, suggestive/sexy clothing is "mildly NSFW." Full nudity, regardless of context, is "very NSFW."
(It may be different in Europe.)
If that would be grounds for firing, even after describing the context of the article, then you decidedly do not work at a fairly liberal software company.
It seems perfectly consistent to me to be 'liberal' and have a 'no (non work related) naked pictures at work' policy under the auspices of a zero-tolerance sexual harassment policy. No one needs to look at naked pictures at work, and they could plausibly make someone uncomfortable in a sexual way.
Now, you could argue that the modern liberal hippie philosophy is that sex is natural and no one should be offended by it and it is just our Puritanical baggage which makes it otherwise, and maybe I'd agree with you. But you could also argue that in the context of our Puritanical baggage, our slut shaming, our last fifty-plus years of Madmen-esque workplace sexual discrimination, we need a period of overly desexualized workplaces before we can shed our Puritanical baggage.
Any sufficiently left-wing policy is indistinguishable from a right-wing policy, and the reverse is also true. Anti-pornography movements present one of the clearest modern illustrations of this phenomenon. The right-winger complains of personal morality, while the left-winger complains about demeaning and objectifying the subjects, but they wind up at basically the same conclusions. Alcohol prohibition showed something very similar around the turn of the century.
It's basically considered a fireable offense under the sexual harassment policy.
However, of course, you can always be fired for demonstrating questionable judgement.
Frankly, it would have been easy to remedy - I was browsing a game forum with image signatures, which is where this image appeared.
Of course, at the time, the HR person didn't like me (I mistook her for my bosses personal assistant when I was hired), so that didn't help. Learned a lot of lessons from that situation - the biggest being "make the HR employees like you".
However, the original point stands - even "liberal software companies" will fire people for less than nudity on your screen.
Sexual harassment isn't just "someone did something that made me feel uncomfortable" -- it's a set of specific and defined offenses, with measurable impacts. You have to have done something which created a hostile environment for your peers, they have to report to management that you are making the environment threatening for them, management has to raise this to your attention and instruct you to stop the offending behavior, and you have to have failed to remedy the situation when you were instructed to.
A zero tolerance policy like you describe would just be a reiteration of the nature of your at-will employment agreement, as what they're saying is that they reserve the right to fire you for doing anything that is questionably dumb. But if you were told that there is a sexual harassment claim against you, you have rights too.
Rights or not, it wasn't realistic to pursue it (an inexperienced 20-something against a multi-million dollar internet giant), and it was enough years ago now that I've gotten something more valuable out of it - experience.
The broader point is that "NSFW" labels carry an implicit caveat emptor warning. Nobody's forcing you to click open a link, and if you believe that you work in an environment with a low tolerance for anything that could be construed as "NSFW," then don't click on a link marked "NSFW" -- even if it's qualified by "mildly," "moderately," "slightly," "possibly," and so forth. If you see the abbreviation "NSFW," you need to take stock of the risks involved in proceeding, and proceed (or not proceed) accordingly.
A corollary: given that one person's definition of NSFW will always differ from another's, it's often best to err on the side of caution.
Personally speaking, I'm thankful I work at the sort of company that wouldn't fire me for viewing this material. And I'm grateful because it's genuinely fascinating material, and the nudity is used for illustrative purposes (and also, conveniently, tucked at the bottom). Of course, if I worked at a bigger or more conservative company, there's no way in hell I would have taken a chance on anything with an NSFW label.
There's a big difference between spending hours at work looking through porn and reading one article which happens to have one nude drawing at the bottom. I find it hard to believe that someone leading a big company in the US can not realize that.
(.|.)I'm put in mind of the old Zawinski quote:
"Some people, when confronted with a problem, think \"I know, I'll use regular expressions.\" Now they have two problems. "
I see stories about teachers being fired for working as strippers on the side, or there's a teacher fired for http://www.parentdish.com/2006/10/02/texas-school-teacher-fi... a child to nude pictures in an Art museum (Texas -- ) but I think this is fanciful. And note that the teacher concerned was no, technically, fired over the art.
Prudishness in the US is pretty ridiculous but the only thing which would be job-threatening here is that you're surfing the web on company time AND the thing you're looking at offends someone.