Response from the site administrator
dr_venture, 15.01.2014
This functionality is available via Zeus/Trenlo's excellent Image Layer extension. Details can be found here:
http://www.fantasygrounds.com/forums/showthread.php?20231-Enhanced-Images-%28layers%29-for-FG-3-0-CoreRPG-%28and-rulesets-based-on-CoreRPG%29