A method and system for generating data in a mobile device is provided. The method includes, outputting an image, stored in the mobile device, to an external screen, capturing the external screen on which the image is being displayed and creating a captured image, comparing the output image with the captured image and extracting an added image from the captured image, and creating data from the extracted image. When the mobile device user writes or draws on an external screen on which the mobile device outputs an image, the mobile device can capture the external screen, create data from the user's input content and store them in the storage unit.