It's been done, but there are legal and ethical issues with photographing children's buttholes.

Scientists Working on Toilet That Identifies You by Your Butthole Many users "wouldn’t, for very good reasons, like cameras pointing up their bottoms.":

https://futurism.com/neoscope/scientists-toilet-identifies-b...

Anal-genital viewing device and method:

https://patents.google.com/patent/US20110083264A1/en

A Very Suggestive Toilet | Alpine Shepherd Boy | Better Call Saul:

https://www.youtube.com/watch?v=dR1m29cNVsc

should use lidar instead of vision