GIMP Plugin Registry

This IFS plugin does exactly what it says - applies an iterated function system over an image, finitely, making it fractal-like. Since images are worth a thousand words:

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This script will take the active path and fractalize it, using a random midpoint displacement algorithm, with the displacement proportionate to the length between nodes. Also the nodes don't move.

Parameters are:  read more »

These scripts are mainly aimed at generating L-system fractals using turtle graphics. As an added bonus, shapes (not fractals) and turtle trails too.
L-system (or shapes, or turtle trails) can be drawn using different tools, including path, and centered/scaled to image/layer/mask.

Save both scripts in your scripts folder, you will find it under Filters -> Render -> Turtle graphics.