Abstract

In its operation, every electrical device generates electromagnetic disturbance signals. They can be due to the operation of components of the device (step motors, heaters, control circuits, or electronic circuits). Quite often such signals have the characteristics of the data processed on such devices. They can have the form of a text. In each case, such signals are undesirable. However, they can be used to reproduce such data or, in other word, to conduct the process of electromagnetic infiltration. In the case of video signals (graphic mode of a computer, a laser printer), then the reproduced data can be presented in the form of graphic images that can be easily assimilated by people. Such images are transformed in order to find the data that is of interest. Reproduction of such data may lead to a disclosure of classified information.
There are many solutions that should counter the process of reproduction of such data. Such solutions are implemented in the design of equipment and influence, to a lesser or greater extent, the appearance of the equipment, as well as the related organizational methods. A new method that can be used in electromagnetic protection of process data is a software solution. It involves the use of appropriate computer fonts. 
The article presents the possibilities related to shaping the form of video signals. For this purpose, appropriate shapes of the letter characters of computer fonts were recommended. Unlike characters in standard fonts (Arial and Times New Roman), they do not have the unique decorative elements (serif), such as hooks, connectors, heels, arches, and ribbons, and consist of only vertical and horizontal lines [5]. There are no slanted and crooked lines. Due to this, the characters are often very similar. This greatly contributes to the impossibility to differentiate between the letter characters in the reproduced image that is filled with noise and numerous disturbances. The graphic elements being searched, having the form of strings of letters, cannot be read. The digital image processing methods intended to improve the quality of the image are quite ineffective.
In search for graphic characters, such as computer font letter and digit characters, one can use methods based on the similarity of the standard with a portion of the analyzed image. However, when special fonts are used, the correlation method generates many false decisions, which also prevents reading text data.