Tags are made from optical films to provide a pattern that is inconspicuous to ordinary observers, but that is detectable by a camera or other imaging device. The pattern is provided by first and second portions of a patterned layer, the first portions selectively filtering at least a portion of blue visible light from other visible light wavelengths. Filtering in the portion of the blue region helps make the pattern inconspicuous. The tags may also include an indicia layer configured to mark a location of the pattern, and a contrast enhancing layer disposed behind the patterned layer and configured to enhance a contrast of the pattern. In some cases, the first portions of the patterned layer may filter optical wavelengths other than blue, such as near-infrared light. The pattern may comprise machine-readable information, e.g., a linear bar code or a 2-D bar code. Associated methods and systems are also disclosed.