1. A method comprising: with a portable, camera-equipped, system, capturing imagery depicting one instance of a device; using information derived from the captured imagery, determining address information for use in communicating with said one instance of the device; using information derived from the captured imagery, authorizing control of said one instance of the device by the camera-equipped system; controlling said one instance of the device using the camera-equipped system, by two-way communication relayed between said system and said device through a remote server, employing said determined address information; wherein other instances of said device also exist, but the camera-equipped system is authorized to control only the one instance of the device from which the imagery was captured; and wherein said capturing act comprises capturing imagery that depicts a feature of the device whose appearance varies over time, wherein said authorizing is based on an appearance of said time-varying feature.