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Buyer visits your site and selects product provider (we recommend to set by default those product provider for which you have "Search by Photo" module).
Then he clicks camera icon in the search bar and downloads a photo of necessary item from his computer.
There is an automatic search and results appear on the page after a while.
Then the buyer chooses the most similar version of the product from the proposed and makes an order if the found product suits parameters (for example, size).