y direction in fig4 the reflected light 17 will also be polarized along the y direction the polarization axis of the second linear polarizer 34 can be oriented along the x direction at a relative angle of 90 degrees with respect to the first linear polarizer 32 such that the reflected light 17 is blocked therefore the label 12 background will appear dark under this type of imaging setup if invisible indicia 14 are present on label 12 they will change the polarization direction of the reflected light this will lead to an incomplete blocking of the reflected light by the second polarizer therefore the invisible indicia will appear bright against a dark background alternatively both linear polarizing filters can be oriented with their polarization axes parallel to each other in this case the label 12 in the absence of invisible indicia i e the background appears bright and any polarization modifying indicia will appear dark in the imager 22 of the camera 18 either of the above described methods will result in a differentiation of the invisible indicia from the background thus allowing visualization of the hidden indicia by the imager 22 optimal differentiation of the invisible indicia from the background will occur when the linear polarized filters are oriented orthogonal to each other or in parallel with each other however differentiation does also occur at other relative orientations of the first and second linear polarizing filters once detected by the imager 22 of the camera 18 the image can be displayed and viewed by an investigator for authentication purposes a static image can be verified visually an alpha numeric code can read.