Ask HN: How do self-checkout cameras recording your face prevent theft?

I've noticed cameras pointed at a customer's face popping up in self-checkout lines at Target and Walmart. Do these actually prevent theft, since they don't seem to record the area where you scan/bag your items?

At first I thought that the cameras might record your face so that the companies could later cross-reference that recording with the time(s) that items were stolen... but if there is a separate such system in place to catch stolen items, I sure don't see it.

(I feel like I should specify that I have no interest in stealing items via the self-checkout line; I'm just annoyed I'm getting recorded if that recording serves no practical purpose.)