Lovela, your ENTIRE signature cannot be any bigger than 250 pixels high. If you don't know how high that is, look at mine. I think mine is sitting right at 249 or 250. Anything higher than that will be CUT OFF automatically. This is why you can't see the rest of your picture.
Try moving your text NEXT to your picture rather than on top of it...
Edit: Nevermind, that won't work either. I just checked the properties on your picture alone and it's 255 high so it's too big. You need to make it smaller by using a picture resizing program or resizing it in paint.