Originally Posted by
xTwoStepx
As an addon author (WIM), I would like to contribute that icons are not allowed to be transmitted. Blizzard specifically put this into place for reasons such as mentioned above as well as to prevent people from spamming certain images.
Images are added client side through WoW's UI.
If a GM whispers you, it simply send text to the default chat frame along with the icon. If it sees {star} it converts it into the texture/image tag.
The only way to get another user to see the images you are sending aside from WoW's preloaded raid icons, is if the other user is using the same addon as yourself to interpret them. In my case.. WIM.
Hope that helped clear things up.