Creates a frame/border outside the image; the frame mirrors the original image.
The menu item appears in
A typical usage is when sending an image to a printer which only prints e.g. 30x20 cm images, while the frame that you want the image in is 22x16 cm. Using this script, you can print a 30x20 cm image, grab a pair of scissors (preferably a shear/guillotine) and then cut off the mirrored frame, without fear of getting a "white border" if your measurements were slightly off. Also useful with e.g. printing to canvases if your print shop charges extra for creating a mirror frame.
Newest version always at https://github.com/unhammer/gimp-fu