Here's my rough sketch on how this could work: a) You track every person from multiple camera angles, it should be "relatively easy" to track the position of e

Here's my rough sketch on how this could work: a) You track every person from multiple camera angles, it should be "relatively easy" to track the position of every customer at all times. I'm not sure if it can handle people in very close proximity (or e.g. after hugging in store) - maybe Amazon actually uses facial recognition to resolve the identities afterwards b) Only one person can enter the gate at once, and it's easy to authenticate the person at the starting point c) Leaving is also a one-way gate, and at that point the system can simply mark the shopping as complete and mail the receipt d) The shelves are specially designed and can sense (maybe with RFIDs) when an item is removed from the shelf, and match that with the person closest to the item. A possible difficulty is handling people who take an item from the back of the shelf (e.g. to get a fresh item).