A hybrid scheme for enhancing recovered image quality in polynomial based secret image sharing by modifyandrecalculate strategy Abstract   A hybrid approach for enhancing the recovered image quality in Shamirxe2x80x99s polynomial based secret image sharing (SIS) is proposed in this paper. To remain computational efficiency, simple modular arithmetic is still used. The fundamental operation in the proposed method is mod P calculation, where P is a prime. A framework for the proposed method is firstly given. Mod PG and mod PS sharing algorithms are included. Then, a modifyandrecalculate strategy for mod PS sharing is proposed to make sure that each generated modular result is within the interval       0  ,   2  N   xe2x88x92  1      . Theoretical analysis on recovered image quality and extensive experiments are conducted. Recommendation on choosing optimal sharing method for different values of N (8xc2xa0xe2x89xa4xc2xa0Nxc2xa0xe2x89xa4xc2xa017) is given.

Blind Multipurpose Image Watermarking Based on Secret Sharing In this paper, in order to accomplish two goals of multimedia authentication and copyright protection, we present a multipurpose watermarking method based on a commonly used cryptographic primitive called verifiable secret sharing scheme. Utilizing this primitive, our scheme achieves blindness meaning that it needs neither the original host image nor the embedded watermark. Our scheme also does not need two distinct watermarks to authenticate the images and at the same time protect their copyright. Experimental results show that the features of the shares, obtained by the used primitive from watermark, enables our method to reconstruct extracted tampered watermarks after various attacks such as JPEG compression, cropping, salt and pepper noise, median filtering, some combined attacks, etc. Comparisons are provided with other multipurpose watermarking methods which primarily aim at protecting copyright of media and authenticating it simultaneously. We also show the superiority of our proposed method to three watermarking methods attaining the goals of copyright protection and authentication.