Several things:
Your links gives me only a jpg image despite the URL name (If it would be transparent, you would get only a completely black image as result with the
rgbimage
style).To plot images with transparency use the
rgbalpha
plotting style:plot 'transparencytest.png' binary filetype=png with rgbalpha
I used the following file
transparencytest.png
for testing, which works fine:Why don't you just put the grid and the border to the
front
layer?