You can use
NPC Code:
changeimgvis index,layer;
.
A layer of 4 or higher (up to 12 or something. Not sure exactly how high it goes unless it was raised...) will display on the screen position.
If you are trying to show something on the direct center of the screen, put 'c' for Center in the formatting part of showtext and use screenwidth/2 and screenheight/2.
Images can use:
NPC Code:
x: screenwidth/2-(imgwidth(image name.png)/2)
y: screenheight/2-(imgheight(image name.png)/2)
If thats for a GUI, use indexes for showimg/showtext that are 200 or higher.
If you don't want it level-based, make it an NPC Weapon.
offline: toweapons -System; (or something) (clientside)
online: addweapon -System; (or something) (serverside)