Patent ID: 8438063

Claim:
A system comprising: a server comprising a processor; and a memory in communication with the server, the memory storing computer instructions that, when executed by the processor, cause the processor to perform operations comprising: receiving a key request from a mobile device performing a transaction with a point-of-sale terminal, the key request being transmitted via a user interface on the mobile device, the key request further comprising a store identifier of a store that operates the point-of-sale terminal, the store identifier being input via the user interface; generating an image comprising a payment key in response to the key request from the mobile device, transmitting the image to the mobile device to be displayed on a display of the mobile device, receiving a bill from the point-of-sale terminal, the point-of-sale terminal comprising a scanner for scanning the image displayed on the display of the mobile device, the bill comprising the payment key extracted from the image, a terminal-input store identifier, and an amount to be charged, determining that the store identifier in the key request submitted by the mobile device is the same as the terminal-input store identifier in the bill submitted by the point-of-sale terminal, and charging a user account the amount to be charged.