I still don’t get it: why would you choose something that’s so hard to change, if ever, for a store ID? It’s convenient but is it secure? There are photos of me waving with my palms out...
Do you really think this is a photo of your palm they're storing? No doubt there are 3D scanners (to map the elevation of your palms, the depth of the lines, etc.), infrared imaging and a slew of other minor sensors. To make this fast, they need to effectively correlate enough of the data to identify you without relying solely on a single thing.
There aren't a bunch of other sensors available.. probably some heat/temperature just to make sure it's a real palm but that's not for uniqueness.