1. A method of preparing a security document comprising the steps of: designating a security image area on the face of a document, wherein said security image area comprises a two-dimensional array of security image blocks, each of said security image blocks is occupied by a set of security image elements and a set of complementary security image elements, said security image elements occupy a security image element portion of each of said security image blocks, said complementary security image elements occupy a complementary security image element portion of each of said security image blocks, said security image elements and said complementary security image elements in respective security image blocks are arranged such that said security image element portion and said complementary security image element portion occupy respective first and second percentages of each of said security image blocks to define respective characteristic relative occupation values for each security image block, and wherein said respective characteristic relative occupation values are substantially equivalent among a plurality of said security image blocks; establishing a target characteristic relative occupation value; establishing respective security image element portions and complementary security image element portions such that said respective security image element portions and said complementary security image element portions occupy said respective first and second percentages of a selected security image block; determining a relative value of said first and second occupation percentages; comparing said relative value of said first and second occupation percentages with said target characteristic relative occupation value; adjusting at least one of said complementary security image element portion and said security image element portion where said comparison indicates a significant disparity between said first and second occupation percentages and said target characteristic relative occupation value, such that said relative value of said first and second occupation percentages substantially corresponds to said target characteristic relative occupation value; and generating a security document including said two-dimensional array of security image blocks, wherein each of said security image blocks is occupied by said security image elements and said complementary security image elements.