This script brings 2 pictures to an exact overlap.
The pictures must be in 2 different layers of the same image.
Get the layer 2 with 50% transparency. This makes both pictures visible in one projection.
You have to tell the script, which 2 points have to overlap. Therefore you stroke a path with a path tool in the image including 4 points. Point 1 will be aligned with point 3 and point 2 will be aligned with point 4.
The points build one path. So you can just click the 4 points consecutively.
More description is in the file.
For a short, quick and dirty video demonstration, please see http://youtu.be/7stawH-egrw