Self-verifying Filter
A transparent part of a multipage document which allows visualizing latent images, texts or codes located on an adjacent page of the document. During the verification process the filter is placed closely to the image area and scrambled data becomes clearly visible.
A self-verifying filter may have the form of a clear window in one of document pages or can be located on a transparent polycarbonate insert stitched into a passport book (fig. 1).
a
b
c
Fig. 1. Belgium. Passport:
а — data page and insert with a self-verifying filter; b — self-verifying filter placed on the holder’s portrait; c — latent scrambled image (personal data), visualized with the help of the filter