"if there are any photos on the internet that will go away it's these, if for no other reason, because they're illegal."
I doubt it; the existence of an FBI database of known child abuse photos suggests that long after these images are identified, they continue to be shared online. Given how many amateur porn websites there are, and how older teenagers can easily pass for adults (thus reducing the likelihood that whatever moderators such websites have will reject the photos), it is almost certain that such photos will continue to be available online long after the girls/boys are adults and have forgotten the whole episode.
I think this argument is a red herring, though. The problem as I see it is not what happens when the photos are out there, the problem is that our notion of sex ed still comes out of the 1950s. We teach children about sex when they are old enough that there is a non-trivial probability they already started having sex. We limit sex ed to information about STIs and a reminder to use a condom (but in New York City, we were not actually shown how to apply one).
We need to update our approach to sex ed to reflect the realities of this century. First of all, children should start receiving some amount of sex ed long before they start having sex; clearly it will need to be explained in a way that is age-appropriate, but we cannot continue to put it off. Second, we must include a discussion about modern technology as it relates to sex -- that includes cameras, computers, and the Internet; if we know that teenagers are doing this, we need to explain to them how to be responsible (in the same way that we say, "use a condom because some STIs last forever," we should be saying, "don't let photos or videos be taken, because they last on the Internet forever"). We need to be frank with kids about these issues, or else they are just going to run wild and "learn" from their friends (who will almost always give them bad advice, betray them, or otherwise "do it wrong").
Yes, technology changes things. That is not a surprise. That is not shocking. If we fail to adapt to those changes, we'll just wind up in the same position as the RIAA and MPAA: crying, whining, and pushing for destructive laws.