This plug-in creates a kind of "burning" effect around a drawable. Both black-on-white and white-on-black source images make sense and create different effects (do not use displace with black-on-white drawables, though ;).
Although the original colour of the image does not matter, supplying a greyscale drawable (though working) does not look very cool.
To install Gimp, copy and paste the appropriate command in to your terminal.
cpanm
cpanm Gimp
CPAN shell
perl -MCPAN -e shell install Gimp
For more information on module installation, please visit the detailed CPAN module installation guide.