Patent ID: 7429062

Claim:
A security feature for a document comprising a first pattern of a plurality of first lines of varying frequency, said first pattern on a first surface of said document, wherein the first lines of varying frequency are repetitive lines with a period of monotonically increasing or decreasing distance; and a second pattern of a plurality of second lines of varying frequency, said second pattern on a second surface of said document, said second surface of said document being opposite said first surface of said document, said second pattern being a reverse of said first pattern, said document being sufficiently transparent wherein said first pattern and said second pattern are see-through such that said first pattern and said second pattern can be viewed superimposed upon each other from said first surface of said document or said second surface of said document, wherein if said first pattern is aligned with said second pattern, said first pattern or said second pattern is visible, if said first pattern is misaligned with said second pattern because of a misalignment between said first and said second pattern on said document, a moire pattern is visible regardless of a magnitude and an orientation of the misalignment where the moire pattern is formed by said first pattern and said second pattern.