This question should be asked here

http://www.tv.com/avatar-the-last-airbender/show/28841/ask-a-question-get-an-answer-ii/topic/13281-479896/msgs.html?tag=board_topics;title;3

To answer ur question, it doesn't appear cause u need image tags.

Just put [img] infront of ur url, and then [/img] at the end, with no spaces