As far as I've been able to determine, eggtopsies are performed on chicks that already died in the shell. That pre-hatch death was observed during candling or opening an egg which had gone well past it's expected hatching date without pipping. Those already dead embryos are then photographed and the conditions of incubation/hatch are described with the photo. I don't know too many people who are deliberately destroying chicks known to still be alive before they've even hatched. Every once in awhile someone will jump the gun and open an egg thinking the chick was already dead in the shell, only to be surprised, but this doesn't happen as part of an experiment.to learn about how it develops, look at all the other developing pictures on how do you think we all have learned so much about how they grow.
Sorry, I just find a profound difference between the phrases "Embryonic Development Experiments" and "Eggtopsy". This kind of information, gathered responsibly and documented well, is already out there and available to anyone who wants to study it. I don't see a need to experiment on live chicks to get another batch of photos.