A computer capable of recognizing gesture commands is disclosed. Suppose that a user makes a gesture of swinging a hand from side to side in front of a camera associated with a computer. A camera module receives frames with shots of the gesture in order. The camera module calculates a gradation difference between corresponding pixels of each frame and a background image to generate a set of binarized differential images. The camera module then combines differential images to generate composite images. In response to a determination that any of the composite images matches a reference pattern, the camera module outputs a computer command. The computer command can be used to control the power state of the computer or start a specific application within the computer.