Dear Diego,
If you have used Fragstats 4.x or 5.x with a free academic license you should use the attribution as indicated under paragraph 5 of the "Fragstats 4.2 (x64) End user license" which you can find at the end of this web page:
www.fragstats.org/index.php/license
If you have a paid Fragstats 5.x license you don't need to use the full attribution but we would be delighted if you decide to mention using Fragstats in your work.
Best regards,
Eduard Ene
