This script is a simple one, yet very useful. The script copies all of the visible
layers in the active image and pastes them into a single layer at the top of the layer stack (the new layer is called "Copied Layers"). This way, if you want to apply additional effects to the "current look" of your layers, you can do so in one simple step and, most importantly, keep your original layers intact. Also, if a selection is active at the time the script is run, only the selected area will be copied/pasted.
You can download it here: http://fence-post.deviantart.com/art/Copy-Visible-and-Paste-Script-72552828
These steps can be done quite easily in GIMP (Copy Visible > Paste > Add New Layer > Anchor Floating Selection), but this really speeds things up.
Essentially, it is GIMP's version of Photoshop's Apply Image option (although I believe the PS version has more options....not sure on that though).
The inspiration for this script is from kward (http://kward1979uk.deviantart.com/art/Merge-copy-28607825
) who wrote the original version, but I've updated it to run in GIMP version 2.4. I've also modified the script to work on Grayscale and Indexed images.
Just download the zip file, double-click the zip file to open, and place the script (scm file) in your GIMP scripts folder (ie....C:\Program Files\GIMP-2.4\share\gimp\2.0\scripts)
Then, go to the main GIMP window (not the image window) and choose the Xtns Menu > Script-FU > Refresh Scripts and it should appear in the Image Window under the Edit Menu > Copy Visible & Paste as Layer