Open a new file, any size (I use 450 wide 140 high[in pixels]) and then take out your render (You will need to resize it, to do that go image>scale image and just mess around with it untill its the size you want) Copy paste it on your blank sig then click layer>new layer twice
Then, on the GIMP toolbar click the layers tab (Looks like white blocks stcked on top of each other) and go to your render layer, copy the main color off your render with the color picker tool (Looks like an eye droper with dark blue liqud coming out) then go to your bottom layer and bucket fill the background with that color
Now go back to your render layer and take an other color from it, then go to the background layer and brush around with one of the brushes you downloaded
Now without changing brushes (I was using PhantasmIII_7) go to the render layer and chosse the smudge tool (Looks like a hand) And lightly smudge the render to blend it with the background
Now go to the top layer and add some text (Optional) I used the blackader ITC font, and set the mode to soft light (Change the mode is right on the layers tab)
Then just add a border, to do that go filters>Decor>Add border change the settings to 1 and the color to black and press okay. Your done, now just go file>save as and chosse the name of your sig, just be sure to put .png at the end.
Final result
Now just upload it to any site like photobucket or imageshack.
I tried to make this as easy to understand as possible, if you have any problems let me know and I will try to help you. Also if you use this please post a link to your results, I would like to see them:D
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