I was responding to the idea of retina scan.
Even with accounts, who is going to hold the data base
A third party isn’t necessary. A hash of retina analysis and some hash key that the voting authority have could be saved. The end result is just a number, like 37162120. Since a retina analysis could not be recreated from the hash, if the list were ever compromised it would not provide sufficient information for someone to recreate the source retina.
Some consumer products already do this with the key being derived by some unique attribute of the hardware. This is done for finger print scans too, so that if someone were able to extract all of the data from a phone that has a fingerprint hash saved the person’t biometrics are not compromised.
All that said, someone would not have to do a great deal of reverse engineering to get elements of someone’s biometrics. People post them all over social media. I myself do not show the palms of my hands in photographs so that someone doesn’t get my finger prints from them. I also avoid putting pictures of myself on social media in general. Many photography devices provide sufficient resolution for getting someone’s finger prints from a photograph and sometimes their iris patterns