1. A method for watermarking a document, comprising: receiving said document; generating an identification number based on said received document; generating a seed based on said generated identification number; generating a first set of numbers using the generated seed; applying a transform to at least a portion of an image of said document to form a transform of said image; defining a second set of numbers comprising transform coefficients from said transform of said image; forming a modified second set of numbers based on said first set and said second set; substituting said modified second set for said second set in said transform of said image to form a modified transform; and applying an inverse of said transform to said modified transform to thereby produce a modified image of said document; whereby said modified image of said document or an output of said modified image constitutes said watermarked document.