A service provider receives, from a merchant device, a geotagged image of a payment instrument, such as a credit card, provided to the merchant by a buyer for payment. It first determines the validity of the payment instrument using the captured image and then assesses the validity of the claimed purchase transaction by comparing the GPS data in the geotagged image, representing the geotagging location, with a separately transmitted GPS data, representing the location of transmitting the geotagged image. For further assessment, it may further compare the time of geotagging the image with the time of transmitting the image. The service provider then determines on the overall validity of the claimed purchase transaction based on the determination on the validity of the payment instrument and the assessment results, and if it determines the purchase transaction is valid, processes requested payment to the merchant's account.