Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
A single unusual photograph without other symptoms is less likely to be an emergency.
Take a few new photographs in similar lighting, with the person looking directly at the camera.
Seek emergency care now for:
After chemical exposure, begin rinsing the eye immediately with plenty of clean, lukewarm water while arranging emergency help.
Arrange a same-day eye assessment if a baby or child has a white pupil that is visible directly or appears repeatedly in photographs.
Contact an optometrist, ophthalmologist, primary care service, or urgent eye service.
Do not wait for the child to report vision problems.
An adult should also seek prompt assessment for a new white pupil, particularly if it affects one eye, is visible in normal light, or comes with a change in vision.
Book an eye examination if the white reflection appears again or you remain concerned.
Every sign above is quoted from the sofidex article on Pupil - white. If you are not sure, err upward — it is always reasonable to be checked.