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Clearly you never actually done Tech projects in large corporate environments if you think complex shit is implemented across all sites just because it can be done, rather than because the expected profits exceed the cost and the hassle.

Also you seem to be under the impression that the social media guys would just give searchable access to their store of pictures (or provide a search service) to those big companies for free, which is a hilariously naive take on how Tech businesses work.

Automated following customers in a store with overhead cameras for the purposes of studying how they move around and purchase things is only done for some stores and has entirely different requirements for camera positions, external dependencies (no cross-referencing with external data to ID anybody is needed) and acceptable error rates (the data is not for selling to others so the error rates can be higher), because they don't need to actually ID anybody to extract "human movement patterns" out of that data and it's fine if the system confuses two people once in a while because there is no external customer of that data getting pissed off when the same person is reported as making purchases in two places at the same time or other stupidly obvious false positives.

Meanwhile matching the list of items bought with payment information, both of which already get sent from the tellers to the backend systems (for purposes of inventory tracking and accounting), is easy peasy and has a very low error rate.

You're ridding a massive Dunning-Krugger there in thinking you're the expert.