In this paper, we describe an intelligent user interface designed for camera phones to allow mobile users to specify the object of interest in the scene simply by taking two pictures: one with the object and one without the object. By comparing these two images, the system can reliably extract the visual appearance of the object, which can be useful to a wide-range of applications such as content-based image retrieval and object recognition. Categories and Subject Descriptors H.5.2 [User Interfaces]: Input devices and strategies, I.4.6 Segmentation. General Terms Human Factors Keywords Object recognition, computer vision, mobile application