They are using an app https://countthings.com/ This seems rather a simple task, however, the app is expensive ($100 per month per device) and limited with the templates for things it can count [1]. [1] https://countthings.com/en/counting-templates
It's easy to do it in an unreliable way. 1000$ a year doesn't seem very expensive if your business depends on it and you're saving a lot of time like in the OP.
> and limited with the templates for things it can count
It seems very specialized towards certain businesses, if you have a specific use case that isn't covered I'm guessing you can probably contact them and see if they can add it?