Abstract: A system uses multimedia data, such as photo of part or whole receipt, records of payment process, and/or signature inputted directly on the touch-phone, as the proof of offline transaction. The multimedia data are uploaded with tags to a center server via internet or wireless network. This system could prove that costumer has finished a transaction such as purchase, which could be a key element for the offline Cost-Per-Action (CPA) advertisement mode, reservation and/or incentive system. This multimedia signature could also be used in authorizing consumers to perform buyer reviews. The mobile devices, which can support multimedia input and output, internet access, location-awareness, and/or touch screen, such as iPhone and gPhone, could be employed for this system.