There are literally thousands of gimp tutorials out there, many concentrate on
Here's what I'd do.
1. Create your new image using the desired dimensions (make it slightly wider
than you need, you can crop it later)
2. click on the gradient tool. Choose foreground colour white, choose
background colour grey
click and drag the gradient tool from the top of the image to the bottom.
3. Choose green as foreground colour, use the rectangular selection tool to
select a thin line at the top of the image (doesn't matter if you go the edges
of the image) then click EDIT > FILL WITH FG COLOUR
4. Use the same tool to select a second rectangle further down (again it
doesn't matter if your selection goes off the edges), and fill with FG colour
5. Then choose white as foreground colour. Click EDIT > STROKE SELECTION -
choose line width of the stroke in pixels, click OK.
6. Now crop your image to size.
Bill (via www.gimpusers.com)
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