> This should help you out:
>
> http://www.tek-tips.com/faqs.cfm?fid=6789
>

Actually looks like I'm a bit wrong about that (that's for window
icons)... but this seems to indicate that at least PNG alpha-channel
transparency works.  I couldn't find much info on GIF transparency.

http://docstore.mik.ua/orelly/perl3/tk/ch17_11.htm

-Jonathan Nielsen