Visual Cryptography is an encryption technique for visual information such as images or text, based on the secret sharing problem. The secret is encrypted in such a way that its decryption is very simple since there is no need for any mathematical calculations: it is done automatically by the human eye. Furthermore, the secret is completely safe since it cannot be revealed by any unauthorized opponent, even one with infinite computational power. The first concrete definition of k out of n visual secret sharing schemes was stated in “Visual Cryptography” by Moni Naor and Adi Shamir along with specific applications and extensions of the initial model. Two more constructions and properties of k out of n visual secret sharing schemes are presented in “Constructions and Properties of k out of n Visual Secret Sharing Schemes” by Eric R. Verheul and Henk C. A. Van Tilborg. Additionally, an introduction to the notion of coloured visual secret sharing schemes is introduced.