This is a script for The GIMP, a image manipulation program. Basically it consists in drawing circles with sequencial numbers inside, so some can "label" parts of a image to reference in another document.
To install it, just move the script to your local scripts directory, in Unix systems it is located at ~/.gimp-2.x/scripts. I don't know about Windows.
If GIMP is opened, just select Filter -> Script-Fu -> Refresh menu. If Gimp is not open, just open it. The menu associated with the script will appear on Script-Fu -> Mark Number Circles.
Before starting, select your foreground and background color. Foreground color will be text color and background color will be circle color.
First you need to draw, on your image, a path with the Path/Vector tool. Don't worry about it being a Bezier curve or whatever, but place the nodes precisely where you want the labels to appear.
After drawing the path, select the Script-Fu -> Mark Number Circles and watch a circle and a number appear in every node of your path.