invisible watermark

What is the difference between visible and invisible digital watermarks?

Visibility is a term associated with the perception of the human eye. A watermarked image in which the watermark is imperceptible, or the watermarked image is visually identical to its orginal constitutes a invisible digital watermarking. Examples include images distrubuted over internet with watermarks embedded in them for copyright protection. Those which fail can be classified as visible digital watermarks. Examples include logos used in papers in currencies.