Quoting Rob Antonishen <rob.antonis...@gmail.com>:
> there is such a plugin. I think I saw it in the Meet the Gimp forums.
I wrote the following script a while back for a coin collector who
wanted to easily crop his scans and rotate them so that the coin was
The interface I used was to click-drag a path from the top of the coin
to the bottom. The resulting path had only one anchor (at the coin's
top) but the control handle was used as the second point.
The script would require some modification but might provide a kludgy
functionality for those needing it.
A discussion over the evolution of the script took place on the
Gimp-developer mailing list