I had previously created a script-fu to automatically emulate the results of shooting on expired Polaroid 600 instant film that included the undeveloped corners that results from old film stock with not enough developer/fix to completely cover the image area:
At the bottom of that script page I had alluded to a border script I created that more faithfully reproduced the textures embossed on actual polaroid 600 film.
Then I promptly forgot all about it.
Well, I was playing around this afternoon and re-discovered this bit of script-fu, and figured I might as well release it into the wild!
This script will take your image and use the image width as the basis for creating a polaroid border over your image. It may take a few minutes to run, as it does a lot to create the embossed pattern, but in the end I think it might be worth it! I also re-calculate the size of the emboss pattern based on your image dimensions as well, so it should scale somewhat ok.
Once installed, you'll find the option to run it under Colors on your menus.
The resulting border should look like this: