In watermarking, changes in the stego object must
have no effect on the watermark. Imagine if you had
an illegal copy of an image that you would like to
manipulate in various ways. These manipulations can
be simple processes such as resizing, trimming or rotating
the image. The watermark inside the image
must survive these manipulations, otherwise the attackers
can very easily remove the watermark and the
point of steganography will be broken.