If I wanted to use the icon of a palading as an image on ground, I would export it with war3 viewer. The I would open it in GIMP and rescale the image to 63x63 then resize the canvas to 64x64 (if the original image was 64x64). You might have to do some .blp to .tga conversions.
There is a program called button manager or something, can't remember if has a feature of adding the transparent borders.