As has been pointed out countless times on this website in the past: There's no biometric sensors that are guaranteed to be free from tampering. There's no way

As has been pointed out countless times on this website in the past: There's no biometric sensors that are guaranteed to be free from tampering. There's no way to prove that the bits and bytes that say "I scanned person X's iris" actually corresponds to a legitimate iris scan. There's no way to stop someone from going town to town with their own iris scanners and claiming they need to scan eyes for the census or vaccines or any number of other things that people might think are real, only to use those scans to accept the money you mentioned in your comment. There's no way to prevent someone from perturbing those scans slightly to allow them to be re-used for new transactions in the future. Extremely advanced credit card skimmers exist, and those subvert the security of little tiny computers embedded in the credit cards. If you think a picture of an iris is any better, I've got an NFT of a bridge to sell you.