Signature Banners question

[Threewolves]

I read the information that states a signature banner must be 720 x 120 pixels or less. So, I made a banner. Saved the jpeg. Uploaded it to a free hosting place. But when I come back here to try and add it to my signature it only previews as the code. Is that correct, or am I doing something wrong? I'm no web guru by any stretch of the imagination. Any help would be appreciated.