WATERMARK DETECTION.

摘要

A WATERMARK IS ASSUMED TO BE EMBEDDED IN A SUSPECT IMAGE IF THERE IS A GIVEN AMOUNT OF CORRELATION BETWEEN THE SUSPECT IMAGE (I) AND THE WATERMARK (W). THE RELIABILITY OF SUCH A WATERMARK DETECTION METHOD IS CONSIDERABLY IMPROVED BY DISTORTING (2) THE SUSPECT IMAGE IN SUCH A WAY THAT A DISTROYED IMAGE (I) IS OBTAINED WHICH RESEMBLES THE SUSPECT IMAGE WHILE THE WATERMARK IS DESTRIYED. THE DISTORTED IMAGE IS THEN SUBSTRACTED (3) FROM THE SUSPECT IMAGE TO OBTAIN A RESIDUAL IMAGE (Q) IN WHICH THE WATERMARK IS MORE DOMINANT. THE DISTORTION MAY BE A SPATIALLY-VARIANT DISTORTION SUCH AS STRETCHING, SHRINKING, SHEARING OR ROTATION. EMBODIMENTS ARE DISCLOSED IN WHICH THE DISTORTED IMAGE IS OBTAINED BY SUBJECTING THE SUSPECT IMAGE TO A NON-LINEAR TRANSFORM OR FILTER OPERATION.(FIG 1)