I've never used photofiltre .. nor have I used "the GIMP" .. but, the GIMP is the closest thing to photoshop out there .. my guess would be, they've tried to be a "poor man's photoshop" from the outset .. due to the cost of photoshop
you can get photoshop for @ $300 via a student discount
in case you haven't poked around the tutorials gallery .. there are a number of excellent guides in there ..
Booleen, Booleen, Booleen, Boooooleeeeen
I'm begging of you please don't take my man
Booleen, Booleen, Booleen, Boooooleeeeen
Please don't take him just because you can