Educational example of masking textual information in a photographic signal

Abstract

The paper presents a steganographic method of masking textual information in photo files. Concealment is implemented in Python. The introduction of individual letters of the text into the image is carried out by the method of "least significant bit". The program can be used for both educational and practical purposes. The Pillow graphics library was used to implement the program. This is not a specialized library for steganographic needs. The use of this library makes it possible to visualize the mechanism of hiding information in the lessons, while the conciseness of the program code gives the possibility to demonstrate it in the classroom setting. It is also important for educational purposes, that working within the Pillow library allows you to see the state of an empty and filled container at the level of individual bits. To assess the practical value of the program, it was tested with texts of different lengths and with containers (photographs) of various kinds. The experiment showed the correct reproduction of texts. Careful visual examination of the empty and correspondingly filled containers (photographs) revealed no differences or suspicions of text bookmarks. Of course, if the party who intercepted the masked message has guesses about how the text is hidden, then this text is easily revealed. Therefore, it is obvious, that the use of the program for practical purposes requires additional manipulations in the code, in particular related to the order of implementation of the text and the choice of location. It is also desirable to additionally encrypt the text with at least a simple method. Such encryption is possible with the usage of a separate program. Analysis of photographs and manipulation with them at the level of individual bits also has educational value in terms of disclosing a method of capturing the corresponding physical signal. The latter gives an explanation of the methods of encoding static images, noise level, the magnitude of the useful physical signal, and the limits of sensitivity of human vision