A loyalty network enables customers to use their mobile devices to participate in a merchant's customer loyalty program. When a customer conducts a transaction, the merchant's point-of-sale (POS) system generates a code image containing transaction information. The POS system may print the code image on a transaction record (such as a bill or receipt) provided to the customer, and/or may display the code image on a display screen. The customer can then photograph/scan the code image with their mobile device, which sends the transaction information and authentication information to a loyalty program server. The loyalty program server may use this information to credit the customer's loyalty program account, and may, in some cases, interact with the POS system to enable loyalty program credits to be redeemed. In some embodiments, the transaction information may alternatively be conveyed to the mobile device using Near Field Communications.