US Patent 11006021 Non-copy correlation mark

A method for rendering a correlation mark on a recording medium can involve encoding a pattern based on a correlation effect color based on a color recipe that includes a high density of one primary color and a mid-to-low density of at least one other primary color, and adjusting the pattern to ensure that the encoding is lost in a resulting rendering of a correlation mark embedded with the pattern. The pattern imposed on the correlation mark is not readily visible in an original without a decoding key. The correlation mark can include a frequency that is sufficiently high so that a copy of the correlation mark may not reproduce with the pattern.