It doesn't have to do with what I think. That is what they do. Why don't you put any amount of effort into verifying what I said instead of insulting me like you think I just made it up?

You don't think that loss prevention would be doing that stuff regardless of whether they had employed cashiers at registers or not? Loss prevention has been around since long before self checkout lanes, doing the same things they're doing now. They already pay those guys. Self checkout is still cheaper if they don't also have to pay a dozen cashiers.

Also, you seem to be imagining a whole fbi crime scene setup in every store for a job that's basically handled per location by 2 guys and a computer.

A "database" doesn't have to be (and usually isn't) centralized across stores. "Hard drives" can be a single multi-terabyte hdd in the age we're in now. "Programming" is just out of the box software they teach their prevention guys to use. The facial recognition and knowing items part comes built into the self checkout machine.

You must not be an engineer either, because an engineer would understand that the cheaper option isn't necessarily lower tech.

Again, take 10 minutes and learn how to utilize a search engine. It's not something they want people to know, but it's also not exactly a secret. Target pioneered the kind of loss prevention techniques big box stores use today.