citing gimp in research?

Hi,

Sorry if this is not quite the right place to post this, but I wanted to make sure it got viewed by someone who could answer my question. I am using gimp in my research (astronomical image processing) for various reasons, and I was wondering if there was a way to cite gimp. It performs an important step in my algorithm (it's not like I'm just using it to touch up plots) so I think it definitely deserves a citation, but I'm not sure how to do this. So please let me know if there's a way I can cite gimp.

Thanks, Cam