Textures of the game are saved in .tex files and described by .xml files. For better compression tecniques you always should combine multiple textures to reach sizes of a power of 2. This will bring performance and reduce the memory usage by computers.
Example:
You get a texture of 200 x 200 pixel. The next power of 2 would be 256 x 256 pixels. If you got graphics of a size between 1 and 56 pixel you can combine them to one image. After that you have to describe the single pictures in the xml file.
Basic Knowledge
For texture creation you need some basic knowledge about textures. Textures are always calculated by width and length. To create a correct texture the width and length has to set by a power of 2!