Background transparency can be set for an ArcIMS Image Service by modifying the *.axl file for that service.
Image Services that generate GIF or PNG images support one transparent color. JPEG does not support transparency.
- Open the *.axl file in a text editor.
- Find <PROPERTIES> in the *.axl file.
- Add BACKGROUND with the color and transcolor attributes. When complete it should look like this:
<BACKGROUND color="255,255,255" transcolor="255,255,255" />
For transparency, the color and transcolor should be the same. Note that all pixels of the specified color become transparent, not just the background.