WT is right, you can always upgrade the board.  You just won't be able to have any texture on the parts of the board that receive player colors, which in this case is 100% of your image. You'll basically be using your image as a template.  Here's a down and dirty way to make a working image.

1. Load your picture in the editor.
2. Create a new layer
3. Make sure your picture is on the bottom layer.
4. In the new layer draw a border all around the X (Usually in Black). Make sure that the line is at least 3 or 4 pixels wide and is NOT anti-aliased (anti-aliasing creates multiple shades of your color - a No-no because they won't fill.)
5. Draw lines (preferably thinner) inside the x to create the borders between territories. Make sure the lines are at least 2 pixels wide, and that the pixels are contiguous horizontaly or vertically (pixels that are only touching diagonally will bleed.).
6. Use the paint can to fill the different territories with different colors. Don't use a brush - You'll likely miss pixels or accidentally paint over a line.  If when filling a territory an adjacent territory fills, then you haven't drawn your lines correctly.

When you're done, You shouldn't be able to see any of the original image. Of course, you can skip steps 2 and 3 and just draw right on top of your picture destructively, but you really should try to get use to using layers in your editor.