Posting pictures?
Once you join a game, you will also be able to select a picture for your character from the existing gallery, if you would like -- that's the picture that appears to the left of posts near the character name in games.
However, you can't do this until you have been added to the game.
As part of your RTJ, you can only post a picture using the code that badpenny mentioned, or you can also simply copy the picture's URL as a link that the GM can click on to follow.