I believe the GP is referring to price look-up codes (https://en.wikipedia.org/wiki/Price_look-up_code). These are often applied via sticker to the produce, as shown in the Wiki images. Every self-checkout system I have used has allowed me to directly type in the PLU for produce, which is what a human cashier would normally do as well.
Additionally, my personal experience with things like this is that human cashiers aren't any better than me at looking up produce in the absence of a PLU code. In fact, I'm generally better because I know what I picked up (or intended to pick up), so I just look for the right name.
it's 4021 apple, because it has a sticker. So you try to scan tiny barcode (if one is present, you can see it on bananas) but if it's missing or dirty, you enter 4-digit PLU by hand. It's very simple and fast:
but yeah, if your store has no number stickers and multiple types of apples I can imagine self-checkout being a major pain. (I can think of a few ways to make this easier -- like provide a roll of stickers next to each variety so customer can attach them to the bag themselves -- but I've never seen this implemented)
at that point, is it really stealing to just make your best guess? are they going to detain you because you input an apple that is $0.04c cheaper than the real one?
Additionally, my personal experience with things like this is that human cashiers aren't any better than me at looking up produce in the absence of a PLU code. In fact, I'm generally better because I know what I picked up (or intended to pick up), so I just look for the right name.