Chin-Chen Chang Tzu-Chuen Lu Yi-Hsuan Fan A Bit-Level Visual Secret Sharing Scheme for Multi-Secret Images Using Rotation and Reversion Operatations. 83-101 2007 Intelligent Multimedia Data Hiding: New Directions http://dx.doi.org/10.1007/978-3-540-71169-8_4 series/sci/2007-58 db/series/sci/sci58.html#ChangLF07