The present invention provides methods and apparatus for imparting a multiplicity of watermarks onto a digitized image. The image includes a plurality of pixels, wherein each of the pixels includes brightness data that represents one brightness value if the image is monochrome, or a plurality of brightness data values if the image has multiple colors. In one aspect it provides for imparting more than one watermark into the digitized image comprising the steps of providing the digitized image, and multiplying the brightness data associated with at least one of the image pixels by a plurality of predetermined brightness multiplying value. Another aspect of the present invention is to provide a method for generating a composite watermark and imparting on a plurality of copies of a digitized image a different composite watermark into each copy. Also provided is a method for detecting one or more of the watermarks in the composite.