How do UPC/EAN Bar Codes Work?
When you go to sell your product at a retailer (i.e. Whole Foods, Amazon, Google etc.), that retailer will have you fill out a product information form. On that form is where you will put your company and product details as well as your 12-digit UPC (Or 13-digit EAN) bar code number. The retailer then manually enters that information into their inventory management computer. This way, when they scan your bar code at the register (or on their site), it calls up that form in their system and gives you credit for the sale.
In other words, the bar code is simply a link between your product and the product information form you fill out for each store that sells your product. The bar code number & bar code image itself does not contain any hidden data, names, prices etc.
Each store, website, database and P.O.S. system will be private, internal, and is usually not publicly editable. This means that in order for you to get into a store or get your data onto a particular website that you want, you will need to manually contact that store/site and ask them what you need to do to manually upload your data so that it appears on their system/servers.