Starting with ETS 5.6, icons can be used at the following elements in addition to or instead of texts:
The individual icons must be quadratic, with size at least 32x32 pixels, in 32 bit RGBA format, stored as PNG files.
All icons used in a application program have to be contained in a single ZIP file, with all PNG files in the root directory of the ZIP structure.
The icon file has to be added to the manufacturer's Baggage element and referenced in the Icon File property of the ApplicationProgram. In the MT project, the file has to be added to M-manufid\Baggages directory (or a subdirectory thereof).