Post some code, and upload your image(s).
Some things to remember...
SET IMAGE COLORKEY works an all images loaded after the command runs.
Objects have transparency settings.
Here is some code to demonstrate that SET OBJECT COLORKEY works on images mapped on objects.
' first we draw a purple square
' with a green cross centered on it
ink rgb(255,0,255),0
box 0,0,100,100
ink rgb(0,255,0),0
box 40,20,60,80
box 20,40,80,60
'make green the transparent color
set image colorkey 0,255,0
'grab the image
get image 1,0,0,100,100,1
'make a cube
make object cube 1,10
'setup the transparency on the object
set object transparency 1,1
' and the culling of the backsides
set object cull 1,0
'apply the image
texture object 1,1
'move the camera
autocam off
position camera 5,10,-10
point camera 0,0,0
do
turn object left 1,0.1
loop
