1. A method for extracting a bit-string from an image, comprising: capturing the image of an encoded bit-string using a camera-equipped device; locating a center of the captured image; determining a direction of travel in the image from the center of the captured image; determining a first thickness corresponding to a value of 0 and a second thickness corresponding to a value of 1; detecting rings in the captured image along the direction of travel from the center, and for each ring: measuring a thickness of the ring to identify it as having the first thickness or the second thickness; and appending to a bit-string a value of 0 if the ring has the first thickness corresponding to the value of 0; or appending to the bit-string a value of 1 if the ring has the second thickness corresponding to the value of 1; and storing the completed bit-string.