A method for authenticating an object that includes providing a label (12) with invisible indicia (14) printed with optically active material on a reflective substrate; providing a device that has a digital camera (18) having a light source (20), an image sensor (22), a first polarizing filter (24) having a first orientation, and a second polarizing filter (26) having a second orientation; illuminating the label with the light from the light source through the first polarizing filter; forming an image with the image sensor using reflected light from the label wherein the reflected light passes through the second polarizing filter prior to reaching the sensor; wherein the second polarizing filter makes the invisible indicia visible; and authenticating the object.