Neither, I'm a student, but am interested in how both sides would deal with photographs which are "just" breasts or vaginas, without any other parts of the subject being visible.
Jmundy - I probably haven't done this sort of case for nearly a decade now thankfully (for either side). However I'd be surprised if those sort of images weren't discounted in the majority of cases. Obviously, this would depend on circumstance though. They might not be discounted if they appeared to be being taken by the individual in question, rather than downloaded, or there was some other information to "support" the case as a whole (or warrant more scrutiny/resources). I'm pretty certain that if your case was just limited to a few images of questionable age, with only genitalia exposed, such that it was far from certain what the age was, that the case would never make it past the CPS over here, and get to court.
There are obviously going to be exceptions to this, as in the distant past I've also been instructed for the defence in the past, on a relatively weak case, with a few pictures of questionable age, and which swiftly was dropped once examined, as there was no realistic chance of prosecution.
I know former colleagues have described in some cases paediatricians (or some kind of expert in the field) being asked to try to age people in photos (vaguely remember being to do with proportions/ratios of bones or suchlike) but I don't know how concrete that is/was and I suspect the expense would rarely be deployed unless in a particular case of significance (rather than just someone with a few pictures). If it was just genitalia I imagine this would be pretty difficult to say with certainly from an image (but maybe science has moved on).
It sounds a bit cold, but I think, like most things in this field, it'll come down to resources. I.e. the significance/strength of the case, whether an expert is likely to be able to give a definitive on the age range or not, and therefore whether it's likely to strengthen a case beyond the point of doubt or not.
About 5 years ago I did research in this area to see if we could, indeed, determine the age of an individual based upon pupil measurements in selfie photographs. Long story short, based on our data, pupils (or any other facial measurement at that) are not a good determinant of determining age beyond adolescence. In children the measurements the numbers are consistent and COULD be a factor, but again, this is shaky ground because you have to factor for values such as lighting (lux), etc. etc.Â
Below is a link to request the paper (for free) and read deeper into our work. FYI- there might be more work in this space since we did this research in 2015:
Feel free to contact me off-list if you I could be of any assistance to you.
-Josh Brunty