Wireless devices and methods employ steganography for a variety of purposes. An exemplary application is a battery-powered cell phone, having, e.g., a microphone, a speaker, a modulator, an antenna, and an RF amplifier. In such application, steganographic techniques can be employed to encode, or decode, signals processed by the phone. Some embodiments use an image sensor to capture watermarked image data. The phone can respond to detection of such marked imagery by overlaying distinctive graphics on a cell phone display screen. Such graphics may be positioned within the display, and affine-warped, in registered relationship with the position of the watermarked object, and its affine distortion, as depicted in the image data.