Do I need the _i images?

I"ve been looking at my error logs and noticed my gui's seem to give me some errors loading my button images.:

setContent(): Invalid control: StartupGui
Engine initialized...
keyboard0 input device created.
mouse0 input device created.
game/client/ui/StartupGui.gui (50): Unable to find object: 'IntroProfile' attempting to call function 'delete'
Could not locate texture: game/client/ui/main_menu/start_i
Could not locate texture: game/client/ui/main_menu/server_i
Could not locate texture: game/client/ui/main_menu/options_i
Could not locate texture: game/client/ui/main_menu/credits_i

For my button images, they are png and I have _n _h and _d used to present the highlighted forms, etc. What is the _i used for? Do I NEED to have them even? Now that I think about it, maybe they are for INACTIVE, but what if I don't care to make buttons inactive. Does it mess up the engine if I don't include the extra images anyway?