Although I tend to agree with this stance from a purely theoretical point of view, lets try and flip it a bit: Male teacher showing a 16 and a 17 year old girl a picture of his chest and abs because he's been working out; they had brought up the topic of exercise and he wanted to show them the results. Does that seem weird?
What if it were a male teacher showing off the results of some penis-related surgery to male students? Would that suddenly be different? You're welcome to say "No", but I would strongly believe that anyone who wouldn't acknowledge the difference would be lying to themselves if they didn't feel something amiss, subconsciously.
Again, from a purely theoretical point of view, this could make some amount of sense or be considered acceptable if it were done in a vacuum of just a single motivation that was the contributing factor here, but in many cases there are other motivations that come into play, like testing boundaries before blatant sexual assault can occur. I am not trying to claim that that is what was occurring here, but if it was - which I do strongly suspect that it was - suddenly the issue might not be so trivial. I guess what I'm trying to say is that ulterior motives play just as much of a role in situations like this as the actual act does, if not more so.
Additionally, it is absolutely a widely known nation-wide for teachers to have a certain amount of fear and restraint around students specifically because of problems like this. Having a job is nice. Not being on a sex offenders list is doubly nice. If a teacher mysteriously no longer has that kind of visceral reaction towards their students, I would argue that any teacher that would knowingly bring in nude photographs of themselves and show it to students should be closely monitored by the police and sent to seek psychiatric help, if not outright having their teaching license revoked. Regardless of opinions on the state of student-teacher relations in the US, I would hold a very strong suspicion towards any teacher that does not maintain that wary sense of distrust towards their students because of the way our legal system works.
Generally speaking, I like to believe that most people are good, and maybe the way this story was presented was not even close to what actually occurred, but...I can't help but feel that there was more bad then good in this story. Sure, it's possible it was all just a big, stupid mistake and the teacher just "wasn't thinking" that day, but I can't help but feel that if I were in her position I would have...I don't know, ran it by the administrative faculty first. "Oh hey, I'm bringing in naked photos of myself to show to my students tomorrow. I'm not going to get fired for that, right?". Something, you know? You don't just do that sort of thing and don't expect their to be repercussions because of it. Basic logic and ass covering should have applied here but it just didn't for unknown reasons, and that is what makes me so suspicious of her motivations.