| 摘要 |
<p>A method for protecting against duplication of a document with a color copier comprises providing a background color on a document having an average reflectance value and printing on the background with a contrast color having a spectral characteristic which modulates the average reflectance value by no more than 5 % and has an average value equal to the average reflectance value. The contrast color is printed with a printing medium that allows activation by a rub and reveal action or by application of intense light.</p> |
