Arbitrariness of the square mapping: The square mapping presents the necessary square reliance and more prominent the haphazardness of the square mapping the more noteworthy would be the security of the plan. In any case, this doesn't ensure that two adjoining squares are not mapped to close by obstructs since the all out number of squares of a picture is just limited. At the point when the degree of altering is enormous, the square mapping may likewise bomb the identification and recuperation.
Alter identification exactness: When the square size is huge if a couple of pixels in the square are altered, the whole square is named altered which thusly influences the nature of the recouped picture. Further, assume that square highlights of k are inserted in square l and that of l in square j. On the off chance that square l is altered, at that point, alter identification of square k and j is troublesome as in simple crisscross of the highlights at the beneficiary's end can't help alter recognition. To address this issue a few plans [4] [12] and so forth installed confirmation bits of the square in a similar square, however reclamation bits in the mapped square. At the point when a square An and its mapped square B wherein highlights of square An are inserted are both seen as altered then recuperation gets troublesome and this circumstance is named as alter fortuitous event issue. Progressively better arrangements were proposed in [3] [16] [2].
Nature of recouped picture: When altered locale is broad, the alter occurrence issue happens more as often as possible than any other time in recent memory and the nature of the recuperated picture is influenced. To conquer the alter incident issue double watermarking, double repetitive ring structure were proposed. [5][6] for example two duplicates of the pressure code are installed with the goal that another opportunity for recouping the square is accessible.
7.2 SELF-EMBEDDING BASED SCHEMES
Lin, Hsieh and Huan [4] separated picture into number of non-covering squares of size 4 x 4 and the watermark length of 8 bits comprised 6 rebuilding bits and 2 confirmation bits for each non-covering 2 x 2 picture hinder that is a piece of a 4 x 4 square.
The six reclamation bits are the 6MSB of the square power normal and of the 2 confirmation bits one was equality bit of the 2 x 2 square and the other piece showed if the normal force of the 2 x 2 square in the 4 x 4 square is more prominent than the normal force of the 4 x 4 square.
Utilizing a straight square guide, a square grouping of 4 x 4 obstructs, A–›B–›C..is created to such an extent that the watermark of a square is inserted in the quickly succeeding square in the succession. The watermark bits of a 2 x 2 square of a 4 x 4 square An is inserted in the LSB of the relating 2 x 2 square of 4 x 4 square B.
