1) Convert the file ICON_TEMPLATE_STARTER.blp to a .bmp or .jpg using Warcraft3 Viewer. 2) Open the file with your image editing software. 3) While maintaining the integrity of the border, paint in the black area.
OR
3a) Open any image file and edit it to suit your needs. 3b) Resize the image to 56X56, then copy and paste it into the ICON_TEMPLATE_STARTER.
4) After you are satisfied with step #3, (if in Photoshop) open the warcraft3icondocument.psd. 5) Drag the desired layer from the .psd directly to the center of your image.
6) Save the file with a new file name. Ex: BTNScarfWholeCountries.jpg DISBTNScarfWholeCountries.bmp 7) Re-convert it back into a .blp.