A grainy image of your palm from a surveillance camera capture is not going to expose biometric data. Your hand needs to be close enough to make out the detail required. Then tying that to your identity is very hard and takes manhours, not something you can replicate at scale. You’re giving them your palm print/vein scan tied to your identity on a plate. It’s very irresponsible.
> A grainy image of your palm
I really doubt getting a reasonably good image of my hand is tough for Amazon. But they don't really need my palm at all; most of the point of that was probably that it'd be much freakier to normies if the self-checkout just said "hi Bob!" when you got close via facial recognition.
> Then tying that to your identity is very hard and takes manhours…
That seems deeply unlikely. I'm probably on 50 different cameras at a Whole Foods, some of which I'd never notice, and at some point I have to check out, which ties all that footage to a credit card and my Prime account if I don't want to pay the non-deal prices for everything.