With the rapid development and diffusion of smart phone applications, mobile users are able to use various useful mobile services in humdrum life. Especially, interesting applications like QR code using camera module in a smart phone are developed continuously nowadays. We realized that the size and shape of shooting objects taken by a smart phone camera module are very different according to their types and versions of the android-based smart phone in the process of developing applications for measuring the shooting object using camera module of a smart phone. In this paper, we investigate the major differences among smart phone types and system versions when we take specific object with camera module of smart phones, analyze the various characteristics of camera modules that influencing the real size of the shooting object taken by a smart phone, and apply them to the development of the smart camruler application.