There are just a few technologies for tracking object-tagged items: Barcode and RFID are at the top of the list. Each has its strengths & weaknesses but the biggest problem is that they can only be scanned at close range. (Note that some long-distance RFID solutions exist such as those used for car toll systems like EZ-Pass but these are expensive and require large, self-powered tags)
Some new work coming out of MIT’s Media Lab may change this. Called Bokode, the system uses the Bokeh optical effect which maps how rays entering an out-of-focus camera lens will converge onto the camera’s sensor.
To see the details, you’ll have to watch the attached video, but in essense the “tag” consists of an LED with an encoded optical pattern and a small cheap lens. An out-of-focus camera will see the data on the tag’s pattern, whether it is a digital code, an image, text or whatever. What’s more, the camera can also determine the angle of the object by doing some tricky optical calculations (which I don’t understand yet).
The tech is still in the development stage, but there is a development WIKI to exchange information among those interested in working more with it. Give it a read – looks like really fun stuff!